Absolute encoder

ABSTRACT

An absolute encoder preferable in being made compact is provided.The absolute encoder includes a worm gear (101c) that rotates in accordance with rotation of a main spindle, and a worm wheel (102a) of which a central axis is perpendicular to a central axis of the worm gear (101c), the worm wheel engaging with the worm gear (101c). The worm gear (101c) is formed using a first material, and the worm wheel (102a) is formed using a second material different from the first material.

TECHNICAL FIELD

The present invention relates to an absolute encoder.

BACKGROUND ART

Conventionally, for various control mechanical devices, rotary encodersare known to be used to detect locations or angles of movable elements.Such encoders include incremental encoders for detecting relativepositions or angles and absolute encoders for detecting absolutepositions or angles. For example, Patent Document 1 describes anabsolute rotary encoder that includes a plurality of magnetic encodersto magnetically detect an angular position of each of a main shaft and alayshaft.

CITATION LIST Patent Document Patent Document 1: Japanese UnexaminedPatent Application Publication No. 2013-24572 SUMMARY OF INVENTION

When the absolute encoder described in Patent Document 1 operates in apoor environment such as a high-temperature environment, backlash may beeliminated due to thermal expansion. Alternatively, displacement or thelike between members due to reduced stress might occur even after theabsolute encoder is out of a high-temperature environment. Also, if arotation speed of a motor is increased, there is demand for preventingreductions in detection accuracy, such as a case where gears areattached to each other when a motor speed is increased, in order toincrease reliability of a device.

Therefore, an objective of the present invention is to provide anabsolute encoder that increases reliability.

An absolute encoder according to an embodiment of the present inventionincludes a first drive gear configured to rotate in accordance withrotation of a main spindle, and a first driven gear of which a centralaxis is perpendicular to a central axis of the first drive gear, thefirst driven gear engaging with the first drive gear. The first drivegear is formed using a first material, and the first driven gear isformed using a second material different from the first material.

Advantageous Effects of Invention

According to the present invention, an absolute encoder that increasesreliability can be provided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of an absolute encoder 100-1 attached to amotor 200 according to a first embodiment;

FIG. 2 is a perspective view of the absolute encoder in which a cover116 is removed from a case 115 illustrated in FIG. 1;

FIG. 3 is a perspective view of the absolute encoder 100-1, asillustrated in FIG. 2, from which a substrate 120 and substrate mountingscrews 122 are removed;

FIG. 4 is a bottom view of the substrate 120;

FIG. 5 is a plan view of the absolute encoder 100-1 illustrated in FIG.3;

FIG. 6 is a cross-sectional view of the absolute encoder 100-1 takenalong a plane that passes through the center of a motor shaft 201 andthat is parallel to an X-Z plane, where a second layshaft gear 138 and amagnetic sensor 90 are illustrated;

FIG. 7 is a cross-sectional view of the absolute encoder 100-1 takenalong a plane that is perpendicular to a centerline of a firstintermediate gear 102 and that passes through the center of a firstlayshaft gear 105;

FIG. 8 is a cross-sectional view of the absolute encoder 100-1, whenviewed approximately from the right side, taken along a plane thatpasses through the center of a second layshaft gear 138 and the centerof a second intermediate gear 133 and that is parallel to a Z-axisdirection;

FIG. 9 is a diagram illustrating a functional configuration of amicrocomputer 121 provided in the absolute encoder 100-1 according tothe first embodiment of the present invention;

FIG. 10 is a plan view of the absolute encoder 100-1 according to amodification of the first embodiment;

FIG. 11 is a cross-sectional view of the first intermediate gear 102taken along a plane that passes through the central axis thereofaccording to the modification of the first embodiment;

FIG. 12A is a cross-sectional view of the first intermediate gear 102taken along a plane that passes through the central axis according toanother modification of the first embodiment;

FIG. 12B is a cross-sectional view of the first intermediate gear 102taken along a plane that passes through the central axis according toanother modification of the first embodiment;

FIG. 13 is a perspective view of an absolute encoder 100-2 attached tothe motor 200 according to a second embodiment of the present invention;

FIG. 14 is a perspective view of the absolute encoder 100-2, asillustrated in FIG. 13, from which a case 15 and a mounted screw 16 areremoved;

FIG. 15 is a perspective view of the absolute encoder 100-2, asillustrated in FIG. 14, from which a substrate 20 and substrate mountingscrews 13 are removed;

FIG. 16 is a perspective view of the absolute encoder 100-2 attached tothe motor 200, as illustrated in the perspective view in FIG. 15, wherethe motor 200 and screws 14 are removed;

FIG. 17 is a plan view of the main base 10, the intermediate gear 2 andthe like as illustrated in FIG. 16;

FIG. 18 is a cross-sectional view of the absolute encoder 100-2, asillustrated in FIG. 17, taken along a plane that passes through thecenter of the intermediate gear 2 and is parallel to the X-Y plane;

FIG. 19 is an enlarged partial cross-sectional view of a bearing 3illustrated in FIG. 18 that is disconnected from the intermediate gear2;

FIG. 20 is a cross-sectional view of the absolute encoder 100-2, asillustrated in FIG. 14, taken along a plane that passes through thecenter of a main spindle gear 1 illustrated in FIG. 17 and that isperpendicular to a centerline of the intermediate gear 2, where thesubstrate 20 and a magnetic sensor 40 are not illustrated in crosssection;

FIG. 21 is a cross-sectional view of the absolute encoder 100-2, asillustrated in FIG. 14, taken along a plane that passes through thecenter of a layshaft gear 5 illustrated in FIG. 18 and that isperpendicular to the centerline of the intermediate gear 2, where thesubstrate 20 and a magnetic sensor 50 are not illustrated in crosssection;

FIG. 22 is a perspective view of multiple components, as illustrated inFIG. 15, from which the intermediate gear 2 is removed;

FIG. 23 is a perspective view of a wall 70, as illustrated in FIG. 22,from which a screw 12 is removed, a leaf spring 11 after the screw 12 isremoved, and the wall 70 with a leaf-spring mounting surface 10 e facingthe leaf spring 11, where the motor 200 and the main spindle gear 1 arenot illustrated;

FIG. 24 is a cross-sectional view of the absolute encoder 100-2, asillustrated in FIG. 14, taken along a plane that passes through thecenter of a substrate positioning pin 10 g and the center of a substratepositioning pin 10 j, as illustrated in FIG. 14, and that is parallel toa Z-axis direction, where a magnetic sensor 40 is not illustrated in thecross section;

FIG. 25 is a view of the substrate 20 illustrated in FIG. 14 when viewedfrom a lower surface 20-1 thereof;

FIG. 26 is a view of the absolute encoder in FIG. 13 from which themotor 200 is removed and that is illustrated when viewed from a lowersurface 10-2 of the main base 10;

FIG. 27 is a perspective view of the case 15 illustrated in FIG. 13;

FIG. 28 is a cross-sectional view of the absolute encoder 100-2, asillustrated in FIG. 13, taken along a plane that passes through thecenter of the substrate positioning pin 10 g and the center of thesubstrate positioning pin 10 j, as illustrated in FIG. 15, and that isparallel to the Z-axis direction, where the motor 200 and the mainspindle gear 1 are not illustrated in cross section;

FIG. 29 is an exploded perspective view of a permanent magnet 8, amagnet holder 6, the layshaft gear 5, and bearings 7 as illustrated inFIG. 21;

FIG. 30 is an exploded perspective view of a permanent magnet 9, themain spindle gear 1, and a motor shaft 201 as illustrated in FIG. 20;

FIG. 31 is a diagram illustrating a manner of a waveform (A) of magneticflux that is from the permanent magnet 9 provided with respect to a mainspindle gear 101 (main spindle gear 1) and that is detected by themagnetic sensor 40, a waveform (B) of magnetic flux that is from thepermanent magnet 9 provided with respect to a first layshaft gear 105(layshaft gear 5) and that is detected by the magnetic sensor 50, and amagnetically interfering waveform (C) of the magnetic flux, from thepermanent magnet 9, on which a portion of the magnetic flux from thepermanent magnet 8 is superimposed as leakage magnetic flux, where themagnetically interfering waveform (C) is detected by the magnetic sensor40;

FIG. 32 is a diagram illustrating a concept of a waveform (A) ofmagnetic flux that is from the permanent magnet 8 provided with respectto the first layshaft gear 105 (layshaft gear 5) and that is detected bya magnetic sensor 50, a waveform (B) of magnetic flux that is from thepermanent magnet 9 provided with respect to the main spindle gear 101(main spindle gear 1) and that is detected by the magnetic sensor 40,and a magnetically interfering waveform (C) of the magnetic flux, fromthe permanent magnet 8, on which a portion of the magnetic flux from thepermanent magnet 9 is superimposed as leakage magnetic flux, where themagnetically interfering waveform (C) is detected by the magnetic sensor50;

FIG. 33 is a diagram illustrating a functional configuration of amicrocomputer 21 included in the absolute encoder 100-2 according to thesecond embodiment of the present invention;

FIG. 34 is a plan view of the absolute encoder 100-2 according to amodification of the second embodiment;

FIG. 35 is a cross-sectional view of the absolute encoder taken along aplane that passes through a central axis of the intermediate gear 2;

FIG. 36 is a diagram illustrating a permanent magnet 9A applicable tothe absolute encoders 100-1 and 100-2 according to the first and secondembodiments; and

FIG. 37 is a diagram illustrating a permanent magnet 9B applicable tothe two absolute encoders 100-1 and 100-2 according to the first andsecond embodiments.

DESCRIPTION OF THE EMBODIMENTS

The configuration of an absolute encoder according to one or moreembodiments of the present invention will be described below in detailwith reference to the drawings. Note that that the present invention isnot intended to be limited by the embodiments.

First Embodiment

FIG. 1 is a perspective view of an absolute encoder 100-1 attached to amotor 200 according to a first embodiment of the present invention. Inthe following description, an XYZ orthogonal coordinate system isemployed. An X-axis direction corresponds to a horizontal right-leftdirection, a Y-axis direction corresponds to a horizontal back-frontdirection, and a Z-axis direction corresponds to a vertical up-downdirection. The Y-axis direction and Z-axis direction are eachperpendicular to the X-axis direction. The X-axis direction may beexpressed by using the word of leftward or rightward, the Y-axisdirection may be expressed by using the word of forward or backward, andthe z-axis direction may be expressed by using the word of upward ordownward.

In FIG. 1, a state of the absolute encoder viewed from above in theZ-axis direction is referred to as a plan view, a state of the absoluteencoder viewed from the front in the Y-axis direction is referred to asa front view, and a state of the absolute encoder viewed from the sidein the X-axis direction is referred to as a side view. Description forthe above directions is not intended to limit an applicable pose of theabsolute encoder 100-1, and the absolute encoder 100-1 may be used inany pose. Note that illustration of the tooth shape is omitted in thedrawings.

FIG. 2 is a perspective view of the absolute encoder in which a cover116 is removed from a case 115 illustrated in FIG. 1. FIG. 3 is aperspective view of the absolute encoder 100-1 illustrated in FIG. 2from which a substrate 120 and substrate mounting screws 122 areremoved. FIG. 4 is a bottom view of the substrate 120. FIG. 5 is a planview of the absolute encoder 100-1 illustrated in FIG. 3. FIG. 6 is across-sectional view of the absolute encoder 100-1 taken along a planethat passes the center of a motor shaft 201 and that is parallel to anX-Z plane, where a second layshaft gear 138 and a magnetic sensor 90 areillustrated. FIG. 7 is a cross-sectional view of the absolute encoder100-1 taken along a plane that is perpendicular to a centerline of afirst intermediate gear 102 and that passes the center of a firstlayshaft gear 105. FIG. 8 is a cross-sectional view of the absoluteencoder 100-1, when viewed approximately from the right side, takenalong a plane that passes the center of a second layshaft gear 138 andthe center of a second intermediate gear 133 and that is parallel to aZ-axis direction. In FIG. 8, illustration of the case 115 and cover 116are omitted.

Hereinafter, the configuration of the absolute encoder 100-1 will bedescribed in detail with reference to FIG. 1 to FIG. 8. The absoluteencoder 100-1 is an absolute-type encoder that determines a rotationamount of a main spindle of the motor 200 through multiple revolutionsand outputs the rotation amount. The motor 200 may be, for example, astepping motor or a DC brushless motor. As an example, the motor 200 maybe applied as a drive source that drives a robot such as for anindustrial robot, via a speed reduction mechanism, such as wave gearing.A motor shaft 201 of the motor 200 protrudes from both sides of themotor 200 in the Z-axis direction. The absolute encoder 100-1 outputsthe rotational amount of the motor shaft 201 as a digital signal. Notethat the motor shaft 201 is an example of a main spindle.

The absolute encoder 100-1 is provided at an end of the motor 200 in theZ-axis direction. The shape of the absolute encoder 100-1 is notparticularly restricted. In the embodiment, the absolute encoder 100-1has an approximately rectangular shape in a plan view, and has a thin,wider rectangular shape in an extending direction (Hereafter referred toas an axial direction. In the first embodiment, the axial direction is adirection parallel to the Z-axis direction.) of a main spindle, in eachof a front view and a side view. That is, the absolute encoder 100-1 hasa flat cuboid shape in the Z-axis direction.

The absolute encoder 100-1 includes the hollow, square tubular case 115that houses an internal structure. The case 115 includes a plurality(e.g., four) of outer walls, e.g., an outer wall 115 a, an outer wall115 b, an outer wall 115 c, and an outer wall 115 d that surround atleast the main spindle and an intermediate rotating body. The cover 116is fixed to end portions of the outer wall 115 a, the outer wall 115 b,the outer wall 115 c, and the outer wall 115 d of the case 115. Thecover 116 has an approximately rectangular shape in a plan view and is aplate-like member that is axially thin.

The outer wall 115 a, the outer wall 115 b, the outer wall 115 c, andthe outer wall 115 d are coupled in this order. The outer wall 115 a andthe outer wall 115 c are provided parallel to each other. Each of theouter wall 115 b and the outer wall 115 d extends to side ends to theouter wall 115 a and the outer wall 115 c, and the outer wall 115 b andthe outer wall 115 d are provided parallel to each other. In thisexample, the outer wall 115 a and the outer wall 115 c extend in theX-axis direction in a plan view, and the outer wall 115 b and the outerwall 115 d extend in the Y-axis direction in a plan view.

The absolute encoder 100-1 includes a main base 110, the case 115, thecover 116, a substrate 120, a leaf spring 111, and a plurality of screws164. The main base 110 is a base that rotatably supports rotating bodiesand gears. The main base 110 includes a base 110 a, a plurality (e.g.,four) of pillars 141, and a shaft 106, a shaft 134, and a shaft 139.

The base 110 a of the main base 110 is a plate-like portion that is onthe motor 200-side of the absolute encoder 100-1, and extends in theX-axis direction and Y-axis direction. The case 115 having a hollowcylindrical shape is secured to the base 110 a of the main base 110 by aplurality (e.g., three) of screws 164.

The pillars 141 disposed on the main base 110 are approximatelycylindrical portions each of which protrudes in an axial direction thatis away from the motor 200, relative to the base 110 a. The pillars 141support the substrate 120. The substrate 120 is secured to protrudingends of the pillars 141, by using the substrate mounting screws 122. InFIG. 2, the substrate 120 is provided in a manner of covering aninterior of the encoder. The substrate 120 has an approximatelyrectangular shape in a plan view, and is a printed wiring board that isaxially thin. A magnetic sensor 50, a magnetic sensor 40, a magneticsensor 90, and a microcomputer 121 are mainly provided on the substrate120.

The absolute encoder 100-1 also includes a main spindle gear 101, a wormgear 101 c, a worm wheel 102 a, a first intermediate gear 102, a firstworm gear 102 b, a worm wheel 105 a, a first layshaft gear 105, a secondworm gear 102 h, and a worm wheel 133 a.

The absolute encoder 100-1 also includes a second intermediate gear 133,a fourth drive gear 133 d, a fourth driven gear 138 a, a second layshaftgear 138, a permanent magnet 8, a permanent magnet 9, a permanent magnet17, the magnetic sensor 50, the magnetic sensor 40, the magnetic sensor90, and the microcomputer 121.

The main spindle gear 101 rotates in accordance with rotation of themotor shaft 201 and transmits the rotation of the motor shaft 201 to theworm gear 101 c. As illustrated in FIG. 6, the main spindle gear 101includes a first cylindrical portion 101 a that fits the outer peripheryof the motor shaft 201, and includes a disk portion 101 b with which aworm gear 101 c is formed, and a magnet holding portion 101 d that holdsthe permanent magnet 9. The magnet holding portion 101 d has acylindrical recessed shape that is provided at a middle portion of thedisk portion 101 b and an upper end surface of the first cylindricalportion 101 a. The first cylindrical portion 101 a, the disk portion 101b, and the magnet holding portion 101 d are integrally formed such thatthe central axes thereof approximately coincide with one another. Themain spindle gear 101 can be formed of various materials, such asresinous materials or metallic materials. The main spindle gear 101 isformed of, for example, a polyacetal resin.

The worm gear 101 c is an example of a first drive gear that drives theworm wheel 102 a. In particular, the worm gear 101 c is a worm gear ofwhich the number of threads is 1, and that is formed on the outerperiphery of the disk portion 101 b. A rotation axis line of the wormgear 101 c extends in the axial direction of the motor shaft 201.

As illustrated in FIG. 5, the first intermediate gear 102 is a gear thattransmits rotation of the main spindle gear 101 to each of the wormwheel 105 a and the second intermediate gear 133. The first intermediategear 102 is rotatably supported about a rotation axis line La, by theshaft 104, where the rotation axis line La extends approximatelyparallel to the base 110 a. The first intermediate gear 102 is anapproximately cylindrical member that extends in a direction of therotation axis line La thereof. The first intermediate gear 102 includesa base 102 c, a first cylindrical portion 102 d with which a worm wheel102 a is formed, a second cylindrical portion 102 e with which a firstworm gear 102 b is formed, and a third cylindrical portion 102 f withwhich a second worm gear 102 h is formed. A through-hole is formed in aninterior of the first intermediate gear 102, and the shaft 104 isinserted through the through-hole. The shaft 104 is inserted through ahole formed in each of the support 110 b and the support 110 c that isprovided on the base 110 a of the main base 110, to thereby rotatablysupport the first intermediate gear 102. Grooves are provided proximalto both ends of the shaft 104 that respectively protrude outwardly fromthe support 110 b and the support 110 c, and a stopper ring 107 and astopper ring 108 for prevention of the shaft 104 from coming out arefitted to the respective grooves, thereby preventing the shaft 104 fromcoming out.

An outer wall 115 a is provided on the side of the first intermediategear 102 opposite to the motor shaft 201. An outer wall 115 c isprovided on the side of the first intermediate gear 102 where the motorshaft 201 is provided, so as to be parallel to the outer wall 115 a. Thefirst intermediate gear 102 may be disposed such that the rotation axisline La thereof is directed to any direction. The rotation axis line Laof the first intermediate gear 102 may be provided in a plan view in therange of 5° to 30°, relative to an extending direction of the outer wall115 a that is provided on the side of the first intermediate gear 102opposite to the motor shaft 201. In the example of FIG. 5, the rotationaxis line La of the first intermediate gear 102 is inclined at an angleof 20°, relative to the extending direction of the outer wall 115 a. Inother words, the case 115 includes the outer wall 115 a that extends, ina plane view, in a direction inclined at an angle in the range of 5° to30°, relative to the rotation axis line La of the first intermediategear 102. In the example of FIG. 5, an inclination Ds of the extendingdirection of the outer wall 115 a, relative to the rotation axis line Laof the first intermediate gear 102, is set to indicate 20°.

In the first embodiment, the base 102 c of the first intermediate gear102 has a cylindrical shape, and each of the first cylindrical portion102 d, the second cylindrical portion 102 e, and the third cylindricalportion 102 f has a cylindrical shape of which the diameter is greaterthan that of the base 102 c. A through-hole is formed in the center ofthe first intermediate gear 102. The base 102 c, the first cylindricalportion 102 d, the second cylindrical portion 102 e, the thirdcylindrical portion 102 f, and the through-hole are integrally formedsuch that central axes thereof approximately coincide with one another.A second cylindrical portion 102 e, a first cylindrical portion 102 d,and a third cylindrical portion 102 f are disposed in this order, atlocations spaced apart from one another. The first intermediate gear 102can be formed of various materials, such as resin materials or metallicmaterials. In the first embodiment, the first intermediate gear 102 isformed of a polyacetal resin.

Each of the support 110 b and the support 110 c is a protrusive memberthat protrudes from the base 110 a in the positive Z-axis direction, bycutting and raising of a portion of the base 110 a of the main base 110.A hole through which the shaft 104 of the first intermediate gear 102 isinserted is formed in each of the support 110 b and the support 110 c.Further, the grooves are provided proximal to both ends of the shaft104, which respectively extend from the support 110 b and the support110 c, and the stopper ring 107 and the stopper ring 108 for preventionof the shaft 104 from coming out are respectively fitted into thegrooves, thereby preventing the shaft 104 from coming out. By such aconfiguration, the first intermediate gear 102 is rotatably supportedabout the rotation axis line La.

The leaf spring 111 will be described. When the first worm gear 102 band the second worm gear 102 h drive respective worm wheels, a reactionforce is applied in the axial direction Td of the first intermediategear 102, and the position of the first intermediate gear 102 in theaxial direction Td might change. In view of the point described above,in the first embodiment, the leaf spring 111 for applying a preloadingforce to the first intermediate gear 102 is provided. The leaf spring111 applies the preloading force in a direction of the rotation axisline La of the first intermediate gear 102, to the first intermediategear 102 to thereby reduce changes in the position of the axialdirection Td. The leaf spring 111 includes a mounting portion 111 battached to the base 110 a of the main base 110, and includes a slidingportion 111 a that extends from the mounting portion 111 b and thencontacts a hemispherical protrusion 102 g. The mounting portion 111 band the sliding portion 111 a are each formed of a spring materialhaving a thin plate shape, and a base of the sliding portion 111 a isbent at an approximately right angle relative to the mounting portion111 b.

As described above, when the leaf spring 111 directly contacts andpresses the hemispherical protrusion 102 g of the first intermediategear 102, the first intermediate gear 102 is preloaded in the axialdirection Td. Further, a sliding portion 102 i of the first intermediategear 102 contacts the support 110 c of the main base 110, and thesliding portion 102 i slides. Thus, changes in the position of the firstintermediate gear 102 in the axial direction Td can be reduced.

In the first embodiment, the direction of a given reaction force to beapplied from the worm wheel 105 a of the first layshaft gear 105 due torotation of the first worm gear 102 b engaged with the worm wheel 105 aof the first layshaft gear 105 is set to be opposite to the direction ofa given reaction force to be applied from the worm wheel 133 a of thesecond intermediate gear 133 due to rotation of the second worm gear 102h engaged with the worm wheel 133 a of the second intermediate gear 133.In other words, the tooth shapes of the respective worm gears are setsuch that components of the resulting reaction forces, in the axialdirection Td, to be applied to the first intermediate gear 102 areinverted with respect to each other. Specifically, inclining directionsof the teeth at the respective worm gears are set such that componentsof the reaction forces to be applied, in the axial direction Td, to thefirst intermediate gear 102 are inversely oriented with respect to eachother. In this case, a small resultant reaction force in the axialdirection Td is obtained in comparison to a case where directions ofcomponents, in the axial direction Td, of the reaction forces to beapplied to the first intermediate gear 102 through the worm gears are inthe same direction, and thus the preloading force of the leaf spring 111can be thereby reduced. Accordingly, rotation resistance of the firstintermediate gear 102 is reduced, thereby enabling smooth rotation.

The above-described method is effective when sliding resistance causedby engagement of the worm gear 101 c of the main spindle gear 101 withthe worm wheel 102 a of the first intermediate gear 102 is relativelylow, and further, a small force to be applied, in the axial directionTd, to the first intermediate gear 102 due to rotation of the mainspindle gear 101, is obtained in comparison to a reaction force to beapplied to the first intermediate gear 102, through the worm wheel 105 aof the first layshaft gear 105 and the worm wheel 133 a of the secondintermediate gear 133. In contrast, when sliding resistance caused byengagement of the worm gear 101 c of the main spindle gear 101 with theworm wheel 102 a of the first intermediate gear 102 is relatively high,the following method is effective.

In FIG. 5, when the main spindle gear 101 rotates to the right, a forceacts rightward on the first intermediate gear 102, due to slidingresistance caused by engagement of the worm gear 101 c of the mainspindle gear 101 with the worm wheel 102 a of the first intermediategear 102, and thus the first intermediate gear 102 is to be movedrightward. At this time, when forces generated, in the axial directionTd, through the worm gears at both ends of the first intermediate gear102 are set to be offset by the method described above, a rightwardacting force on the first intermediate gear 102 is relatively increaseddue to sliding resistance caused by the engagement of the worm gear 101c of the main spindle gear 101 with the worm wheel 102 a of the firstintermediate gear 102, as described above. In order to prevent the firstintermediate gear 102 from moving rightward, against the rightwardacting force on the first intermediate gear 102, a pressing force by theleaf spring 111 needs to be increased. In such a case, slidingresistance associated with the sliding portion 111 a of the leaf spring111 and the hemispherical protrusion 102 g of the first intermediategear 102 to be contacted and pressed by the sliding portion 111 a, aswell as sliding resistance associated with the sliding portion 102 i,which is located at the end of the first intermediate gear 102 toward adirection opposite to the hemispherical protrusion 102 g, and thesupport 110 c, are increased, thereby increasing the rotationalresistance of the first intermediate gear 102.

When the main spindle gear 101 rotates to the right, each of a reactionforce to act on the first intermediate gear 102 through the worm wheel105 a of the first layshaft gear 105, due to rotation of the first wormgear 102 b engaged with the worm wheel 105 a of the first layshaft gear105, and a reaction force to act on the first intermediate gear 102through the worm wheel 133 a of the second intermediate gear 133, due torotation of the second worm gear 102 h engaged with the worm wheel 133 aof the second intermediate gear 133, is set to a force acting in adirection that enables the first intermediate gear 102 to move leftwardrelative to axial direction Td, and thus a rightward acting force on thefirst intermediate gear 102 can be reduced due to the above-mentionedsliding resistance caused by engagement of the worm gear 101 c of themain spindle gear 101 with the worm wheel 102 a of the firstintermediate gear 102. In such a manner, a smaller preloading force tobe applied to the first intermediate gear 102 can be set by the leafspring 111. Accordingly, rotation resistance of the first intermediategear 102 can be reduced, thereby resulting in smooth rotation of thefirst intermediate gear 102.

In contrast, when the main spindle gear 101 rotates to the left, slidingresistance caused by the engagement of the worm gear 101 c of the mainspindle gear 101 with the worm wheel 102 a of the first intermediategear 102 causes a leftward acting force on the first intermediate gear102, relative to the axial direction Td, and thus the first intermediategear 102 is to be moved leftward. At this time, the reaction forces onthe first worm gear 102 b and the second worm gear 102 h, which are atboth ends of the first intermediate gear 102, are both forces to movethe first intermediate gear 102 rightward. Thus, in this case as well, aleftward acting force on the first intermediate gear 102 can be reduced.Because the preloading force to be applied to the first intermediategear 102 by the leaf spring 111 is constantly a leftward acting forcerelative to the axial direction Td, by reducing the leftward actingforce on the first intermediate gear 102, through engagement of thegears at three locations described above, the entirely leftward actingforce on the first intermediate gear 102 is also reduced. Accordingly,rotation resistance caused by sliding of the sliding portion 102 i atthe left end, as illustrated in the figure, of the first intermediategear 102, as well as sliding of the support 110 c provided on the base110 a of the main base 110, can be reduced.

In FIG. 5, the worm wheel 102 a is an example of a first driven gearthat engages with the worm gear 101 c of the main spindle gear 101. Theworm wheel 102 a is a worm wheel for which the number of teeth is 20 andthat is formed on the outer periphery of the first cylindrical portion102 d. The worm gear 101 c and the worm wheel 102 a constitute a firstworm speed-changing mechanism. The rotation axial line of the worm wheel102 a extends in a direction perpendicular to the axial direction of themotor shaft 201.

When the number of threads for the worm gear 101 c of the main spindlegear 101 is 1, and the number of teeth for the worm wheel 102 a of thefirst intermediate gear 102 is 20, a reduction ratio is 20. That is,when the main spindle gear 101 rotates 20 revolutions, the firstintermediate gear 102 rotates once, expressed by 20÷20.

The first worm gear 102 b is an example of a second drive gear thatdrives the worm wheel 105 a and is a gear of the first intermediate gear102. In particular, the first worm gear 102 b is a worm gear for whichthe number of threads is 5 and that is formed on the outer periphery ofthe second cylinder portion 102 e. The rotation axis line of the firstworm gear 102 b extends in a direction perpendicular to the axialdirection of the motor shaft 201.

In FIGS. 5 and 7, the first layshaft gear 105 is decelerated to rotatetogether with the permanent magnet 8, in accordance with rotation of themotor shaft 201. The first layshaft gear 105 is an approximatelycircular member, in a plan view, that includes the cylindrical shaftreceiving portion 105 b that is rotatably supported by the shaft 106 andthat protrudes approximately perpendicular to the base 110 a of the mainbase 110. The member includes a disk portion 105 c with which the wormwheel 105 a is formed, and a holding portion 105 d with which thepermanent magnet 8 is held.

In FIG. 7, the disk portion 105 c has a disc shape extending radiallyfrom the outer periphery of the shaft receiving portion 105 b. In thefirst embodiment, the disk portion 105 c is disposed at a locationtoward a distal end of the shaft receiving portion 105 b, relative tothe base 110 a. The holding portion 105 d has a cylindrical recessedshape provided at a distal end surface of the shaft receiving portion105 b, relative to the base 110 a, in the axial direction of the diskportion 105 c. The shaft receiving portion 105 b, the disk portion 105c, and the holding portion 105 d are integrally formed such that centralaxes thereof approximately coincide with one another. The first layshaftgear 105 may be formed of various materials, such as resin materials ormetallic materials. In the first embodiment, the first layshaft gear 105is formed of a polyacetal resin.

The worm wheel 105 a is an example of a second driven gear that isengaged with the first worm gear 102 b. In particular, the worm wheel105 a is a gear for which the number of teeth is 25 and that is formedon the outer periphery of the disk portion 105 c. The first worm gear102 b and the worm wheel 105 a constitute a second worm speed-changingmechanism. The rotation axis line of the worm wheel 105 a extends in adirection parallel to the axial direction of the motor shaft 201.

When the number of threads for the first worm gear 102 b of the firstintermediate gear 102 is 5, and the number of teeth for the worm wheel105 a of the first layshaft gear 105 is 25, a reduction ratio is 5. Thatis, when the first intermediate gear 102 rotates five revolutions, thefirst layshaft gear 105 rotates once. Thus, when the main spindle gear101 rotates 100 revolutions, the first intermediate gear 102 rotates 5rotations, expressed by 100÷20, and the first layshaft gear 105 rotatesonce, expressed by 5÷5. Because the first layshaft gear 105 rotatestogether with the permanent magnet 8, when the main spindle gear 101rotates 100 revolutions, the permanent magnet 8 rotates once. That is,the magnetic sensor 50 can identify a rotational amount of the mainspindle gear 101, corresponding to 100 revolutions.

The absolute encoder 100-1 in such a configuration can determine arotational amount of the main spindle gear 101. As an example, when themain spindle gear 101 rotates once, each of the first layshaft gear 105and the permanent magnet 8 rotate one-hundredth, i.e., by 3.6°. Thus,when a rotation angle of the first layshaft gear 105 is less than orequal to 3.6°, a rotation amount of the main spindle gear 101 that isrotated by less than or equal to a single revolution can be determined.

In FIG. 5, the second worm gear 102 h is an example of a third drivegear that drives the worm wheel 133 a and is a gear of the firstintermediate gear 102. In particular, the second worm gear 102 h is aworm gear for which the number of threads is 1 and that is formed on theouter periphery of the third cylindrical portion 102 f. The rotationaxis line of the second worm gear 102 h extends in a directionperpendicular to the axial direction of the motor shaft 201.

In FIG. 5, the second intermediate gear 133 is a disk-like gear thatrotates in accordance with rotation of the motor shaft 201 and thatdecelerates the rotation of the motor shaft 201 to transmit it to thesecond layshaft gear 138. The second intermediate gear 133 is providedbetween the second worm gear 102 h and the fourth driven gear 138 a thatis provided in the second layshaft gear 138. The fourth driven gear 138a engages with the fourth drive gear 133 d. The second intermediate gear133 includes a worm wheel 133 a that engages with the second worm gear102 h of the third drive gear, and includes a fourth drive gear 133 dwhich drives the fourth driven gear 138 a. The second intermediate gear133 is formed, for example, of a polyacetal resin. The secondintermediate gear 133 is an approximately circular member in a planview. The second intermediate gear 133 includes a shaft receivingportion 133 b that is rotatably supported at the base 110 a of the mainbase 110 and includes an extended portion 133 c with which a worm wheel133 a is formed.

In FIG. 5, by providing the second intermediate gear 133, the secondlayshaft gear 138 described below can be thereby disposed at a locationaway from the second worm gear 102 h. Thus, a distance between thepermanent magnet 9 and the permanent magnet 17 can be increased toreduce the effect of leakage flux with respect to each other. Further,by providing the second intermediate gear 133, a greater range ofreduction ratios can be thereby set, and thus design flexibility isincreased.

In FIG. 8, the extended portion 133 c has a disc shape extendingradially from the outer periphery of the shaft receiving portion 133 b.In the first embodiment, the extended portion 133 c is disposed at alocation toward a distal end of the shaft receiving portion 133 b,relative to the main base 110. The fourth drive gear 133 d is formed onthe outer periphery of the shaft receiving portion 133 b, in a regiontoward the base 110 a relative to the extended portion 133 c. The shaftreceiving portion 133 b and the extended portion 133 c are integrallyformed such that central axes thereof approximately coincide with eachother.

The worm wheel 133 a is a gear of the second intermediate gear 133 thatis engaged with the second worm gear 102 h. In particular, the wormwheel 133 a is a worm wheel for which the number of teeth is 30 and thatis formed on the outer periphery of the extended portion 133 c. Thesecond worm gear 102 h and the worm wheel 133 a constitute a third wormspeed-changing mechanism. The rotation axis line of the worm wheel 133 aextends in a direction parallel to the axial direction of the motorshaft 201.

When the number of threads for the second worm gear 102 h of the firstintermediate gear 102 is 1, and the number of teeth for the worm wheel133 a of the second intermediate gear 133 is 30, a reduction ratio is30. That is, when the first intermediate gear 102 rotates 30revolutions, the second intermediate gear 133 rotates once. Accordingly,when the main spindle gear 101 rotates 600 revolutions, the firstintermediate gear 102 rotates 30 revolutions, expressed by 600÷20, andthe second intermediate gear 133 rotates once, expressed by 30÷30.

The fourth driven gear 133 d is a transmission element that drives thefourth driven gear 138 a. The fourth drive gear 133 d is provided on theside of the main spindle gear 101 opposite to the first layshaft gear105, and rotates in accordance with rotation of the worm wheel 133 a.The fourth drive gear 133 d is a flat gear for which the number of teethis 24 and that is formed on the outer periphery of the shaft receivingportion 133 b.

In FIG. 8, the second layshaft gear 138 is a disk-like gear, in a planview, that rotates in accordance with rotation of the motor shaft 201and that decelerates the rotation of the motor shaft 201 to therebytransmit it to the permanent magnet 17. The second layshaft gear 138 isrotatably supported about a rotation axis line that approximatelyextends vertically from the base 110 a of the main base 110. The secondlayshaft gear 138 includes a shaft receiving portion 138 b that isrotatably supported at the base 110 a of the main base 110, and includesan extended portion 138 c with which the fourth driven gear 138 a isformed, and a magnet holding portion 138 d with which the permanentmagnet 17 is held. The shaft receiving portion 138 b has a cylindricalshape that annularly surrounds, via a space, the shaft 139 thatprotrudes from the base 110 a of the main base 110.

The extended portion 138 c has a disc shape that radially extends froman outer periphery of the shaft receiving portion 138 b. In the firstembodiment, the extended portion 138 c is disposed at a location of theshaft receiving portion 138 b toward the base 110 a of the main base110. The magnet holding portion 138 d has a cylindrical, recessed shapethat is provided, in the axial direction of the shaft receiving portion138 b, at a distal end surface of the shaft receiving portion 138 b,relative to the base 110 a. The shaft receiving portion 138 b, theextended portion 138 c, and the magnet holding portion 138 d are formedintegrally such that central axes thereof approximately coincide withone another. The second layshaft gear 138 can be formed of variousmaterials such as residual materials or metallic materials. In the firstembodiment, the second layshaft gear 138 is formed of a polyacetalresin.

The fourth driven gear 138 a is a transmission element that is driven bythe fourth drive gear 133 d. The fourth driven gear 138 a and the fourthdriven gear 133 d constitute a speed reduction mechanism. In particular,the fourth driven gear 138 a is a flat gear for which the number ofteeth is 40 and that is formed on the outer periphery of the extendedportion 138 c.

When the number of teeth for the fourth drive gear 133 d is 24, and thenumber of teeth for the fourth driven gear 138 a is 40, a reductionratio is 40/24, i.e., 5/3. When the main spindle gear 101 rotates 1000revolutions, the first intermediate gear 102 rotates 50 revolutions,expressed by 1000÷20, and the second intermediate gear 133 rotates 5/3revolutions, expressed by 50÷30. Thus, the second layshaft gear 138rotates once, expressed by 5/3÷5/3. The second layshaft gear 138 rotatestogether with the permanent magnet 17. Accordingly, when the mainspindle gear 101 rotates 1000 revolutions, the permanent magnet 17rotates once. In such a manner, the magnetic sensor 90 can identify arotational amount corresponding to 1000 revolutions of the main spindlegear 101.

In FIGS. 5 to 8, the permanent magnet 9 is a first permanent magnet, thepermanent magnet 8 is a second permanent magnet, and the permanentmagnet 17 is a third permanent magnet. Each of the permanent magnet 8,the permanent magnet 9, and the permanent magnet 17 (hereafter alsoreferred to as each permanent magnet) has an approximately flat,cylindrical shape in an axial direction thereof. Each permanent magnetis formed of a magnetic material such as a ferritic-based material, orNd (neodymium)-Fe (iron)-B (boron) based material. Each permanent magnetmay be, for example, a rubber magnet containing a binder resin, or abonded magnet. Each permanent magnet has magnetic poles. There is nolimitation to a magnetization direction of each permanent magnet. In thefirst embodiment, as illustrated in FIG. 36 and FIG. 37, two magneticpoles are provided on opposing end surfaces of each permanent magnetfacing the magnetic sensor. A distribution of magnetic flux density ofeach permanent magnet in the rotation direction thereof may be set toindicate a trapezoidal shape, a sinusoidal shape, or a rectangularshape.

Each permanent magnet is partially or entirely housed in a recessedportion formed at a given end of a corresponding rotor, and is secured,for example, with adhesion, a swage, press fit, or the like. Thepermanent magnet 8 is bonded and fixed to the holding portion 105 d forthe first layshaft gear 105. The permanent magnet 9 is bonded and fixedto the magnet holding portion 101 d of the main spindle gear 101. Thepermanent magnet 17 is bonded and fixed to the magnet holding portion138 d of the second layshaft gear 138.

When a shorter distance between permanent magnets is set, a greaterdetection error by a given magnetic sensor might be obtained due to theeffect of leakage magnetic flux from adjacent magnets. In view of thepoint described above, in the example of FIG. 5, in a plan view, thepermanent magnet 9 and the permanent magnet 8 are disposed spaced apartfrom each other, on a sight line Lm that is inclined relative to theouter wall 115 a of the case 115. The sight line Lm corresponds to avirtual line that connects the permanent magnet 8 and the permanentmagnet 9. The permanent magnet 9 and the permanent magnet 17 aredisposed spaced apart from each other, on a sight line Ln that isinclined relative to the outer wall 115 a of the case 115. The sightline Ln corresponds to a virtual line that connects the permanent magnet17 and the permanent magnet 9. In the first embodiment, each of thesight lines Lm and Ln is provided to be inclined relative to the outerwall 115 a, and thus a great distance between the permanent magnets canbe set in comparison to a case where the sight lines Lm and Ln are eachparallel to the outer wall 115 a.

Each of the magnetic sensor 50, the magnetic sensor 40, and the magneticsensor 90 (hereafter also referred to as each magnetic sensor) is asensor that detects an absolute rotation angle in the range of 0° to360° corresponding to a single revolution of a given rotor. Eachmagnetic sensor outputs a signal (e.g., a digital signal) correspondingto a detected rotation angle to the microcomputer 121. Each magneticsensor outputs the same rotation angle as that before interruption ofthe power supply, even when power is interrupted and then is suppliedagain. Thus, a configuration that does not include a backup power supplyis achieved.

As illustrated in FIG. 4, each magnetic sensor is secured to the sameplane, by a method such as soldering or adhesion achieved with respectto a surface of the substrate 120 toward the base 110 a of the main base110. The magnetic sensor 40 is secured to the substrate 120 so as to beat a location facing, via a fixed space, the end surface of thepermanent magnet 9 that is provided with respect to the main spindlegear 101. The magnetic sensor 40 is a first angular sensor that detectsa rotation angle of the main spindle gear 101, corresponding to a changein magnetic flux that is generated from the permanent magnet 9. Themagnetic sensor 50 is secured to the substrate 120 so as to be at alocation facing, via a fixed space, a given end surface of the permanentmagnet 8 provided with respect to the first layshaft gear 105. Themagnetic sensor 50 is a second angular sensor that detects a rotationangle of the first layshaft gear 105, corresponding to a change inmagnetic flux that is generated from the permanent magnet 8. Themagnetic sensor 90 is secured to the substrate 120 so as to be at alocation facing, via a fixed space, a given end surface of the permanentmagnet 17 that is provided with respect to the second layshaft gear 138.The magnetic sensor 90 is a third angular sensor that detects a rotationangle of the second layshaft gear 138, corresponding to a change inmagnetic flux that is generated from the permanent magnet 17.

A magnetic angular sensor with relatively high resolution may be used aseach angular sensor. A magnetic angular sensor is disposed in an axialdirection of a given rotating body so as to face, via a fixed space, endsurfaces of each permanent magnet including magnetic poles. The magneticangular sensor identifies a rotation angle of a given rotor, based onrotation of the magnetic poles, and then outputs a digital signal. As anexample, the magnetic angular sensor includes a detecting element thatdetects magnetic poles, and an arithmetic circuit that outputs a digitalsignal based on an output of the detecting element. The detectingelement may include a plurality (e.g., four) of magnetic field-detectingelements, such as Hall elements or giant magneto resistive (GMR)elements.

The arithmetic circuit may determine a rotation angle by tableprocessing in which a look-up table is used with, for example, adifference or ratio, as a key, between outputs of the plurality ofdetecting elements. The detecting element and arithmetic circuitry maybe integrated on one IC chip. The IC chip may be embedded in a resinthat has a thin cuboid contour. Each magnetic sensor outputs, to themicrocomputer 121, an angle signal that is a digital signalcorresponding to a rotation angle of a given rotor, where the rotationangle is detected through a wiring member not illustrated. For example,each magnetic sensor outputs a rotation angle of a corresponding rotoras a digital signal of multiple bits (e.g., 7 bits).

FIG. 9 is a diagram illustrating the functional configuration of themicrocomputer 121 that is provided in the absolute encoder 100-1according to the first embodiment of the present invention. Themicrocomputer 121 is secured to the surface of the substrate 120 towardthe base 110 a of the main base 110, with a method such as soldering oradhesion. The microcomputer 121 is implemented by a CPU, and acquires adigital signal indicating a rotation angle that is output from each ofthe magnetic sensor 40, the magnetic sensor 50, and the magnetic sensor90, and then calculates a rotation amount of the main spindle gear 101.Each block of the microcomputer 121 illustrated in FIG. 9 represents afunction (function) implemented when the CPU as the microcomputer 121executes a program. In terms of hardware, each block of themicrocomputer 121 may be implemented by an element, such as a centralprocessing unit (CPU) of a computer, or a machine device. In terms ofsoftware, each block may be implemented by a computer program or thelike. In this description, each functional block achieved byco-operation of hardware with software is illustrated. In this regard,it would be understood by those skilled in the art involved with thespecification, that each block can be implemented in various manners byusing a combination of hardware and software.

The microcomputer 121 includes a rotation-angle acquiring unit 121 p, arotation-angle acquiring unit 121 q, a rotation-angle acquiring unit 121r, a table processing unit 121 b, a rotation-amount determining unit 121c, and an output unit 121 e. The rotation-angle acquiring unit 121 qacquires, based on a signal output from the magnetic sensor 40, arotation angle Aq that is angle information indicating a rotation angleof the main spindle gear 101. The rotation-angle acquiring unit 121 pacquires, based on the signal output from the magnetic sensor 50, arotation angle Ap that is angle information indicating a rotation angleof the first layshaft gear 105. The rotation-angle acquiring unit 121 racquires a rotation angle Ar that is angle information indicating arotation angle of the second layshaft gear 138 that is detected by themagnetic sensor 90.

The table processing unit 121 b identifies a rotation speed of the mainspindle gear 101, corresponding to an acquired rotation angle Ap, byreferring to a first relationship table that stores rotation angles Apand rotation speeds of the main spindle gear 101 each corresponding to agiven rotation angle Ap. The table processing unit 121 b also identifiesa rotation speed of the main spindle gear 101 corresponding to anacquired rotation angle Ar by referring to a second corresponding tablethat stores rotation angles Ar and rotation speeds of the main spindlegear 101 each corresponding to a given rotation angle Ar.

The rotation-amount determining unit 121 c determines a first rotationamount through multiple revolutions of the main spindle gear 101, inaccordance with a rotation speed of the main spindle gear 101 identifiedby the table processing unit 121 b, as well as an acquired rotationangle Aq. The output unit 121 e converts the rotation amount of the mainspindle gear 101 through the multiple revolutions, determined by therotation-amount determining unit 121 c, into information indicating therotation-amount, and then outputs the information.

In such a configuration, the function and effect of the absolute encoder100-1 according to the first embodiment will be described.

The absolute encoder 100-1 according to the first embodiment is anabsolute encoder that determines a rotation amount of a motor shaft 201that rotates a plurality of revolutions. The absolute encoder 100-1includes a worm gear 101 c that rotates in accordance with rotation ofthe motor shaft 201, and a worm wheel 102 a that engages with the wormgear 101 c. The absolute encoder 100-1 includes a first worm gear 102 bthat rotates in accordance with rotation of the worm wheel 102 a, and aworm wheel 105 a that engages with the first worm gear 102 b. Theabsolute encoder 100-1 includes a first layshaft gear 105 that rotatesin accordance with rotation of the worm wheel 105 a, and a permanentmagnet 8 that rotates together with the first layshaft gear 105. Theabsolute encoder 100-1 includes a magnetic sensor 50 that detects arotation angle of the permanent magnet 8. In such a configuration, arotation amount of the motor shaft 201 that rotates a plurality ofrevolutions can be determined based on a detected result by the magneticsensor 50. A first worm speed-changing mechanism that includes the wormgear 101 c and the worm wheel 102 a engaging with the worm gear 101 c,as well as a second worm speed-changing mechanism that includes thefirst worm gear 102 b and the worm wheel 105 a engaging with the firstworm gear 102 b, are included, and thus the absolute encoder 100-1 formsa bent transmission path, thereby enabling the absolute encoder to bemade thinner.

An absolute encoder 100-1 according to the first embodiment is anabsolute encoder that determines a rotation amount of a motor shaft 201that rotates a plurality of revolutions. The absolute encoder 100-1includes a first intermediate rotating body 102 that rotates at a firstreduction ratio in accordance with rotation of the motor shaft 201, anda first layshaft gear 105 that rotates at a second reduction ratio inaccordance with rotation of the first intermediate rotating body 102.The absolute encoder 100-1 includes a permanent magnet 8 that rotatestogether with the first layshaft gear 105, and a magnetic sensor 50 thatdetects a rotation angle of the permanent magnet 8. Where, a rotationaxis line of the motor shaft 201 is skew with respect to a rotation axisline of the first intermediate gear 102 and is set to be parallel to arotation axis line of the first layshaft gear 105. In such aconfiguration, the rotation amount of the motor shaft 201 that rotates aplurality of revolutions can be determined in accordance with a detectedresult by the magnetic sensor 50. A rotation axis line of the firstintermediate gear 102 is skew with respect to rotation axis lines of themotor shaft 201 and the first layshaft gear 105, and is perpendicular toeach of the rotation axis lines, in a front view. Thus, the absoluteencoder 100-1 forms a bent transmission path, thereby enabling theabsolute encoder to be made thinner.

The absolute encoder 100-1 according to the first embodiment is anabsolute encoder that determines a rotation amount of a motor shaft 201that rotates a plurality of revolutions. The absolute encoder 100-1includes a speed reduction mechanism that includes a first wormspeed-changing mechanism to rotate a permanent magnet 8 in accordancewith rotation of the motor shaft 201, and includes a magnetic sensor 50that detects a rotation angle of the permanent magnet 8, throughmagnetic poles of the permanent magnet 8. Where, a rotation axis line ofthe motor shaft 201 is set to be parallel to a rotation axis line of thepermanent magnet 8. In such a configuration, a rotation amount of themotor shaft 201 that rotates a plurality of revolutions can bedetermined in accordance with a detected result by the magnetic sensor50. The first worm speed-changing mechanism is included, and a rotationaxis line of the motor shaft 201, as well as the rotation axis line ofthe permanent magnet 8, are set to be parallel to each other. Thus, theabsolute encoder 100-1 can form a bent transmission path, therebyenabling the absolute encoder to be made thinner.

The absolute encoder 100-1 according to the first embodiment includes amagnetic sensor 40 that detects a rotation angle of the motor shaft 201.In such a configuration, a rotation angle of the motor shaft 201 can bedetermined based on a detected result by the magnetic sensor 40. Incomparison to a case where a magnetic sensor 40 is not included, theabsolute encoder 100-1 can increase resolution of identifiable rotationangles of the motor shaft 201.

The absolute encoder 100-1 according to the first embodiment includes asecond worm gear 102 h that rotates in accordance with rotation of aworm wheel 102 a, and includes a worm wheel 133 a that engages with thesecond worm gear 102 h, and a second layshaft gear 138 that rotates inaccordance with rotation of the worm wheel 133 a. The absolute encoder100-1 includes a permanent magnet 17 that rotates together with thesecond layshaft gear 138, and a magnetic sensor 90 that detects arotation angle of the permanent magnet 17. In such a configuration, arotation amount of the motor shaft 201 that rotates a plurality ofrotations can be determined based on a detected result by the magneticsensor 90. The absolute encoder 100-1 can obtain a great range ofidentifiable rotation of the motor shaft 201, in comparison to a casewhere a magnetic sensor 90 is not included.

The absolute encoder 100-1 according to the first embodiment includes afirst intermediate gear 102 that includes a first worm gear 102 b and asecond worm gear 102 h, and a direction of a reaction force applied tothe first intermediate gear 102 due to rotation of the first worm gear102 b is set to be opposite to a direction of a reaction force appliedto the first intermediate gear 102 due to rotation of the second wormgear 102 h. In such a configuration, a resultant reaction force of thereaction forces can be reduced in comparison to a case where directionsof reaction forces are the same.

In the absolute encoder 100-1 according to the first embodiment, anouter diameter of the worm wheel 102 a is set to be smaller than anouter diameter of the worm gear 101 c. In such a configuration, it iseasy to make the worm wheel 102 a thin in comparison to a case in whichthe outer diameter of the worm wheel 102 a is greater.

Hereafter, magnetic interference will be described, where for example,if the main spindle gear 101 and the first layshaft gear 105 aredisposed adjacent to each other, a portion of magnetic flux inducedthrough each of the permanent magnet 8 and the permanent magnet 9 mightinfluence a magnetic sensor that does not correspond to the otherpermanent magnet among the permanent magnet 8 and the permanent magnet9.

FIG. 31 is a diagram illustrating a manner of a waveform (A) of magneticflux that is from the permanent magnet 9 provided with respect to themain spindle gear 101 (main spindle gear 1) and that is detected by themagnetic sensor 40, a waveform (B) of magnetic flux that is from thepermanent magnet 9 provided with respect to the first layshaft gear 105(layshaft gear 5) and that is detected by the magnetic sensor 50, and amagnetically interfering waveform (C) of the magnetic flux, from thepermanent magnet 9, on which a portion of the magnetic flux from thepermanent magnet 8 is superimposed as leakage magnetic flux, where themagnetically interfering waveform (C) is detected by the magnetic sensor40. The vertical axis represents the magnetic flux, and the horizontalaxis represents the rotation angle of the main spindle gear 1. In such amanner, the magnetic sensor 40 desirably detects the waveform (A) above.However, if magnetic interference occurs, the waveform illustrated in(C) above is produced, and thus the waveform could not be detectedaccurately.

Likewise, FIG. 32 is a diagram illustrating a concept of a waveform (A)of magnetic flux that is from the permanent magnet 8 provided withrespect to the first layshaft gear 105 (layshaft gear 5) and that isdetected by a magnetic sensor 50, a waveform (B) of magnetic flux thatis from the permanent magnet 9 provided with respect to the main spindlegear 101 (main spindle gear 1) and that is detected by the magneticsensor 40, and a magnetically interfering waveform (C) of the magneticflux, from the permanent magnet 8, on which a portion of the magneticflux from the permanent magnet 9 is superimposed as leakage magneticflux, where the magnetically interfering waveform (C) is detected by themagnetic sensor 50. The vertical axis represents the magnetic flux, andthe horizontal axis represents the rotation angle of the layshaft gear5. In such a manner, the magnetic sensor 50 desirably detects thewaveform (A) above. However, if magnetic interference occurs, thewaveform illustrated in (C) above is produced, and thus the waveformcould not be detected accurately. Further, magnetic interference mightoccur between the main spindle gear 101 and the second layshaft gear138, as in FIG. 32(C).

The absolute encoder 100-1 according to the first embodiment includes acase 115 including an outer wall 115 a that is disposed on the side ofthe first intermediate gear 102 opposite to the motor shaft 201, and ina plan view, a rotation axis line La of the first intermediate gear 102is inclined at an angle of 20°, relative to an extending direction ofthe outer wall 115 a. According to such a configuration, greatinclination of an arrangement line of each permanent magnet with respectto the outer wall 115 a can be set in comparison to a case where therotation axis line La of the first intermediate gear 102 is notinclined. In such a manner, a greater distance between permanent magnetscan be set. Thus, by increasing a given distance between the permanentmagnets, a portion of magnetic flux generated through each of thepermanent magnet 8, the permanent magnet 9, and the permanent magnet 17can cause reductions in the occurrence of magnetic interference thatinfluences a given magnetic sensor that does not correspond to the othermagnet among the permanent magnet 8, the permanent magnet 9, and thepermanent magnet 17. For example, interference of a portion of magneticflux, as leak magnetic flux, generated through the permanent magnet 9that is provided with respect to the main spindle gear 101, in themagnetic sensor 50 provided in order to achieve its primary purpose ofdetecting changes in magnetic flux that is generated through thepermanent magnet 8 provided with respect to the first layshaft gear 105,can be mitigated. Also, for example, interference of a portion ofmagnetic flux, as leak magnetic flux, generated through the permanentmagnet 8 that is provided with respect to the first layshaft gear 105,in the magnetic sensor 40 provided in order to achieve its primarypurpose of detecting changes in magnetic flux generated through thepermanent magnet 9, can be mitigated. Thus, the effect of leakage fluxthrough adjacent magnets can be reduced.

As described above, the absolute encoder 100-1 according to the firstembodiment includes a first worm speed-changing mechanism that includesthe worm gear 101 c of the main spindle gear 101 and the worm wheel 102a of the first intermediate gear 102, and includes a second wormspeed-changing mechanism that includes the first worm gear 102 b of thefirst intermediate gear 102 and the worm wheel 105 a of the firstlayshaft gear 105. The absolute encoder 100-1 also includes a third wormspeed-changing mechanism that includes the second worm gear 102 h of thefirst intermediate gear 102 and the worm wheel 133 a of the secondintermediate gear 133. For example, a pitch circle of the worm gear 101c is set to be greater than a pitch circle of the worm wheel 102 a, inorder to make the absolute encoder 100-1 compact, while ensuring areduction ratio required for a worm speed reduction mechanism.

In contrast, by setting a greater pitch circle of the worm gear 101 c, acircumferential velocity of a tooth surface is increased, and thusfrictional heat of the tooth surface might be increased. Also, when themotor 200 operates at high speed, frictional heat of the tooth surfacemight be also increased. The motor 200 and absolute encoder 100-1 may bealso used in a high-temperature environment. In such a high-temperatureenvironment, due to thermal expansion of a given gear, backlash of thegiven gear is eliminated and thus tooth clogging might occur. In orderto extend a life of the absolute encoder 100-1, wear resistance of thetooth surface is required to be ensured. In view of the problemdescribed above, the absolute encoder 100-1 according to the firstembodiment is desirably configured as follows. In the followingdescription, the configuration of the absolute encoder 100-1 accordingto a modification of the first embodiment will be described.

FIG. 10 is a plan view of the absolute encoder 100-1 according to themodification of the first embodiment. FIG. 11 is a cross-sectional viewof the first intermediate gear 102 taken along a plane that passesthrough the central axis thereof according to the modification of thefirst embodiment. The absolute encoder 100-1 according to themodification of the first embodiment differs from the absolute encoder100-1 according to the first embodiment, in the main spindle gear 101and the first intermediate gear 102. Other configurations are the same,and duplicate description is omitted.

As illustrated in FIG. 10, the first intermediate gear 102 includes afirst intermediate gear part S1 including a worm wheel 102 a, a secondintermediate gear part S2 including a first worm gear 102 b, and a thirdintermediate gear part S3 including a second worm gear 102 h.

As illustrated in FIG. 11, the first intermediate gear part S1 includesinsert portions S1 a and S1 c. The insert portion S1 a is formed at aportion of the first intermediate gear part S1 toward one end thereof,and has a cylindrical shape that is formed to extend in a direction ofthe central axis of the first intermediate gear part. The insert portionS1 c is formed at a portion of the first intermediate gear part S1toward another end thereof, and has a cylindrical shape that is formedto extend in the direction of the central axis of the first intermediategear part. The second intermediate gear part S2 has an insert receivingportion S2 a into which the insert portion S1 a is inserted. The insertreceiving portion S2 a is formed at a portion of the second intermediategear part S2 toward one end thereof, and extends in a direction of thecentral axis of the second intermediate gear part. The insert receivingportion S2 a has a cylindrical shape that is formed so as to have agreater diameter than that of the insert portion S1 a. The insertreceiving portion S2 a has a bottom S2 b. The third intermediate gearpart S3 has an insert receiving portion S3 a into which the insertportion S1 c is inserted. The insert receiving portion S3 a is formed ata portion of the third intermediate gear part S3 toward one end thereof,and extends in the direction of the central axis of the thirdintermediate gear part. The insert receiving portion S3 a has acylindrical shape that is formed so as to have a greater diameter thanthat of the insert portion Sic. The insert receiving portion S3 a has abottom S3 b.

A bearing S4 is inserted into the insert receiving portion S2 a, and theinsert portion S1 a is further inserted into the insert receivingportion S2 a. The bearing S4 is disposed between the bottom S2 b and anend surface S1 b. Note that each of the end surface S1 b and the bottomS2 b contacts an outer ring of the bearing S4. The shaft 104 illustratedin FIG. 10 is inserted through an inner ring of the bearing S4. By pressfit of the insert portion S1 a into the insert receiving portion S2 a,the first intermediate gear part S1 and the second intermediate gearpart S2 rotate in an integrated manner.

The bearing S5 is inserted into the insert receiving portion S3 a, andthe insert portion S1 c is further inserted into the insert receivingportion S3 a. The bearing S5 is disposed between the bottom S3 b and theend surface S1 d. Note that each of the end surface S1 d and the bottomS3 b contacts an outer ring of the bearing S5. The shaft 104 is insertedthrough an inner ring of the bearing S5. By press fit of the insertportion S1 c into the insert receiving portion S3 a, the firstintermediate gear part S1 and the third intermediate gear part S3 rotatein an integrated manner.

For example, the main spindle gear 101 including the worm gear 101 c,the second intermediate gear part S2 including the first worm gear 102b, and the third intermediate gear part S3 including the second wormgear 102 h may be each formed using a first material. As the firstmaterial, for example, a polybutylene terephthalate resin containing aninorganic filler (hereafter also referred to as “inorganicfiller-containing PBT”) can be used. Note that as the inorganic filler,for example, potassium titanate fiber or the like can be used.

Also, for example, the first intermediate gear part S1 including theworm wheel 102 a, the first layshaft gear 105 including the worm wheel105 a, and the second intermediate gear 133 including the worm wheel 133a may be each formed using a second material. As the second material, apolyacetal resin (hereafter also referred to as “POM natural”) withoutcontaining any filler or the like can be used.

A combination of members and materials is not limited to the combinationdescribed above. When the first intermediate gear part S1 and the mainspindle gear 101 are formed of different materials, it is particularlyeffective, because the first intermediate gear part and the main spindlegear may rotate at high speed.

Note that each of the first material and the second material is notlimited to a resinous material. As long as two types of materials havingdifferent characteristics, including a metallic material such as a brassmaterial, are used, the first material and the second material aresufficient.

Preferably, a coefficient of linear thermal expansion of material of oneamong the main spindle gear 101, including the worm gear 101 c, and thefirst intermediate gear part S1 including the worm wheel 102 a is lowerthan a coefficient of linear thermal expansion of a polyacetal resin.Thus, in comparison to a case where both the main spindle gear 101 andthe first intermediate gear part S1 are each formed of a polyacetalresin, backlash between the worm gear 101 c and the worm wheel 102 a canbe prevented from being eliminated even in a high-temperatureenvironment, thereby preventing tooth clogging due to thermal expansion.Note that when both the material of the main spindle gear 101 and thematerial of the first intermediate gear part S1 are each material havinga lower coefficient of linear thermal expansion than that of apolyacetal resin, it is more preferable from the viewpoint of preventingelimination of backlash or tooth clogging due to thermal expansion.

More preferably, a coefficient of linear thermal expansion of thematerial of the main spindle gear 101 including the worm gear 101 c islower than a coefficient of linear thermal expansion of a polyacetalresin. For example, in use in a high-temperature environment, becausethe worm gear 101 c having a great diameter is provided, a largeabsolute amount of radial expansion is obtained in comparison to a casewhere a worm gear having a smaller diameter is provided. Thus, toothclogging might occur due to elimination of backlash. In view of thepoint described above, when as a material of the main spindle gear 101,a material having a low coefficient of linear thermal expansion is used,elimination of the tooth backlash is prevented more suitably.Accordingly, tooth clogging can be prevented.

Preferably, the material of at least one among the main spindle gear 101including the worm gear 101 c and the first intermediate gear part S1including the worm wheel 102 a is a resin containing an inorganicfiller. By using the resin containing an inorganic filler, a wear volumeof the other material can be reduced. Thus, a life of the first wormspeed-changing mechanism can be extended.

Preferably, a melting point of the material of the main spindle gear 101including the worm gear 101 c is different from a melting point of thematerial of the first intermediate gear part S1 including the worm wheel102 a. For example, when the same material is used for two gears, in acase where a temperature of tooth surfaces thereof is greater than orequal to a given melting temperature, molten resins may crush eachother, thereby resulting in adhesion between the molten resins. Incontrast, when materials having different melting points arerespectively used for two gears, even if a melting point of one gear isreached, a melting point of the other gear is not reached, therebyallowing for reductions in possibility of adhesion between thematerials.

As described above, the relationship between the material of the mainspindle gear 101 including the worm gear 101 c and the material of thefirst intermediate gear part S1 including the worm wheel 102 a has beendescribed. Likewise, the relationship described above can apply to therelationship between the material of the second intermediate gear partS2 including the first worm gear 102 b and the material of the firstlayshaft gear 105 including the worm wheel 105 a. Also, the relationshipdescribed above can apply to the relationship between the material ofthe third intermediate gear part S3 including the second worm gear 102 hand the material of the second intermediate gear 133 including the wormwheel 133 a.

Hereafter, the relationship between the material of the firstintermediate gear part S1 and the material of the second intermediategear part S2 will be described.

Preferably, a coefficient of linear thermal expansion of the material(first material, e.g., an inorganic filler-containing PBT) of the secondintermediate gear part S2 is lower than a coefficient of linear thermalexpansion of the material (second material, e.g., POM natural) of thefirst intermediate gear part S1. The insert portion S1 a of the firstintermediate gear part S1 is configured to be press-fitted into theinsert receiving portion S2 a of the second intermediate gear part S2.In such a manner, thermal expansion of the insert receiving portion S2 acan be lower than thermal expansion of the insert portion S1 a, in thehigh-temperature environment. Thus, the effect of press fit can beprevented from being mitigated due to thermal expansion.

Preferably, tensile break strain of the material (first material, e.g.,inorganic filler-containing PBT) of the second intermediate gear partS2, which is to receive an insert, is smaller than tensile break strainof the material (second material, e.g., POM natural) of the firstintermediate gear part S1, which is to be inserted. Thus, when the firstintermediate gear 102 is assembled such that the insert portion S1 a ofthe first intermediate gear part S1 is press-fitted into the insertreceiving portion S2 a of the second intermediate gear part S2,assembling of the first intermediate gear 102 is facilitated. Also, anegative change in inclination of the axial center of the firstintermediate gear 102, relative to the shaft 104, due to decreases instress, can be reduced. Note that a method of measuring tensile breakstress can be employed by referring to, for example, ISO 527, JIS K7161,ASTM D638, or the like.

As described above, the relationship between the material of the firstintermediate gear part S1 and the material of the second intermediategear part S2 has been described. The same relationship can be applied tothe relationship between the material of the first intermediate gearpart S1 and the material of the third intermediate gear part S3.

Further, the bearing S4 is disposed at a connection portion at which theinsert portion S1 a is press-fitted into the insert receiving portion S2a. The bearing S5 is disposed at a connection portion at which theinsert portion S1 c is press-fitted into the insert receiving portion S3a. The first intermediate gear 102 has a structure supported by thebearings S4 and S5, thereby allowing for reductions in rattling in aradial direction of the first intermediate gear.

At a connection portion at which the insert portion S1 a is press-fittedinto the insert receiving portion S2 a, the bearings S4 and S5 eachhaving greater stiffness than the first intermediate gear part S1, thesecond intermediate gear part S2, and the third intermediate gear partS3, are disposed. In such a manner, the bearings S4 and S5 serve assupports for supporting a structure of the first intermediate gear 102.

Moreover, in comparison to a case where the first intermediate gear 102that includes the worm wheel 102 a, the first worm gear 102 b, and thesecond worm gear 102 h is molded integrally, for a case where the firstintermediate gear part S1 including the worm wheel 102 a, the secondintermediate gear part S2 having the first worm gear 102 b, and thethird intermediate gear part S3 including the second worm gear 102 h aremolded separately, for example, mold design for injection molding isfacilitated, thereby increasing productivity. Also, different materialscan be respectively assigned to the worm wheel 102 a, the first wormgear 102 b, and the second worm gear 102 h.

FIGS. 12A and 12B are cross-sectional views of the first intermediategear 102 taken along a plane that passes through the central axisthereof according to another modification of the first embodiment. Asillustrated in FIG. 12A, a fourth intermediate gear part S6 thatincludes the worm wheel 102 a and the second worm gear 102 h, as well asa second intermediate gear part S2 that includes the first worm gear 102b, may be included. Also, as illustrated in FIG. 12B, a fifthintermediate gear part S7 that includes the worm wheel 102 a and thefirst worm gear 102 b, as well as a third intermediate gear part S3 thatincludes the second worm gear 102 h, may be included.

Second Embodiment

FIG. 13 is a perspective view of an absolute encoder 100-2 attached tothe motor 200 according to a second embodiment of the present invention.In the following description, an XYZ orthogonal coordinate system isemployed, as in the first embodiment. An X-axis direction corresponds toa horizontal right-left direction, a Y-axis direction corresponds to ahorizontal back-front direction, and a Z-axis direction corresponds to avertical up-down direction. The Y-axis direction and Z-axis directionare each perpendicular to the X-axis direction. The X-axis direction maybe expressed by using the word of leftward or rightward, the Y-axisdirection may be expressed by using the word of forward or backward, andthe Z-axis direction may be expressed by using the word of upward ordownward. In FIG. 13, a state of the absolute encoder viewed from abovein the Z-axis direction is referred to as a plan view, a state of theabsolute encoder viewed from the front in the Y-axis direction isreferred to as a front view, and a state of the absolute encoder viewedfrom the side in the X-axis direction is referred to as a side view.Description for the above directions is not intended to limit anapplicable pose of the absolute encoder 100-2, and the absolute encoder100-2 may be used in any pose. In FIG. 13, components provided withinthe case 15 of the absolute encoder 100-2 are illustrated transparently.Note that illustration of the tooth shape is omitted in the drawings.

FIG. 14 is a perspective view of the absolute encoder 100-2, asillustrated in FIG. 13, from which a case 15 and a mounted screw 16 areremoved. In FIG. 14, components provided on the lower surface 20-1 ofthe substrate 20 are illustrated transparently. FIG. 15 is a perspectiveview of the absolute encoder 100-2, as illustrated in FIG. 14, fromwhich the substrate 20 and substrate mounting screws 13 are removed.FIG. 16 is a perspective view of the absolute encoder 100-2 attached tothe motor 200, as illustrated in the perspective view in FIG. 14, wherethe motor 200 and screws 14 are removed. FIG. 17 is a plan view of themain base 10, the intermediate gear 2 and the like as illustrated inFIG. 16. In FIG. 17, arrangement of main components, among multiplecomponents provided in the absolute encoder 100-2, is illustrated. FIG.18 is a cross-sectional view of the absolute encoder 100-2, asillustrated in FIG. 17, taken along a plane that passes through thecenter of the intermediate gear 2 and is parallel to the X-Y plane.

FIG. 19 is an enlarged partial cross-sectional view of a bearing 3illustrated in FIG. 18 that is disconnected from the intermediate gear2. In FIG. 19, in order to facilitate the understanding of thepositional relationship between the bearing 3 and a press-fit portion 2d formed in the intermediate gear 2, the bearing 3 is separated from thepress-fit portion 2 d of the intermediate gear 2. Also, in FIG. 19, inorder to facilitate the understanding of the positional relationshipbetween the bearing 3 and a wall 80 provided on a base 60 of the mainbase 10, the bearing 3 is separated from the wall 80.

FIG. 20 is a cross-sectional view of the absolute encoder 100-2, asillustrated in FIG. 14, taken along a plane that passes through thecenter of a main spindle gear 1 illustrated in FIG. 17 and that isperpendicular to a centerline of the intermediate gear 2, where thesubstrate 20 and a magnetic sensor 40 are not illustrated in the crosssection. In FIG. 20, an attached state of a permanent magnet 9 to themain spindle gear 1, and an attached state of the main spindle gear 1 toa motor shaft 201 are illustrated. Further, in FIG. 20, a state where aworm gear 1 d of the main spindle gear 1 and a worm wheel 2 a of theintermediate gear 2 are engaged with each other is illustrated. FromFIG. 20, it is understood that an upper surface 9 a of the permanentmagnet 9 provided for the main spindle gear 1 is located at a fixeddistance from the magnetic sensor 40, in the Z-axis direction.

FIG. 21 is a cross-sectional view of the absolute encoder 100-2, asillustrated in FIG. 14, taken along a plane that passes through thecenter of a layshaft gear 5 illustrated in FIG. 18 and that isperpendicular to the centerline of the intermediate gear 2, where thesubstrate 20 and a magnetic sensor 50 are not illustrated in the crosssection. In FIG. 21, a state in which a worm wheel 5 a and a worm gear 2b are engaged with each other is illustrated. Further, in FIG. 21, astate where a shaft 6 b of a magnet holder 6 is held by two bearings 7,and a state where the permanent magnet 8 is held by the magnet holder 6are illustrated. Moreover, in FIG. 21, a state where a radially outersurface of a head 6 c provided in the magnet holder 6 is separated froman addendum circle of the worm gear 2 b is illustrated. From FIG. 21, itis understood that a surface 8 a of the permanent magnet 8 provided atthe magnet holder 6 is located at a fixed distance from the magneticsensor 50, in the Z-axis direction. FIG. 21 also illustrates across-sectional shape of a bearing holder 10 d of the main base 10.

FIG. 22 is a perspective view of multiple components, as illustrated inFIG. 15, from which the intermediate gear 2 is removed. FIG. 23 is aperspective view of a wall 70, as illustrated in FIG. 22, from which ascrew 12 is removed, a leaf spring 11 after the screw 12 is removed, andthe wall 70 with a leaf-spring mounting surface 10 e facing the leafspring 11, where the motor 200 and the main spindle gear 1 are notillustrated.

FIG. 24 is a cross-sectional view of the absolute encoder 100-2, asillustrated in FIG. 14, taken along a plane that passes through thecenter of a substrate positioning pin 10 g and the center of a substratepositioning pin 10 j, as illustrated in FIG. 17, and that is parallel toa Z-axis direction, where a magnetic sensor 40 is not illustrated in thecross section.

FIG. 25 is a view of the substrate 20 illustrated in FIG. 14 when viewedfrom a lower surface 20-1 thereof. FIG. 26 is a view of the absoluteencoder in FIG. 13 from which the motor 200 is removed and that isillustrated when viewed from a lower surface 10-2 of the main base 10.The lower surface 10-2 of the main base 10 is a surface opposite to theupper surface of the main base 10 illustrated in FIG. 23. The lowersurface 10-2 of the main base 10 is also a surface facing the motor 200.FIG. 27 is a perspective view of the case 15 illustrated in FIG. 13.

FIG. 28 is a cross-sectional view of the absolute encoder 100-2, asillustrated in FIG. 13, taken along a plane that passes through thecenter of the substrate positioning pin 10 g and the center of thesubstrate positioning pin 10 j, as illustrated in FIG. 15, and that isparallel to the Z-axis direction, where the motor 200, the main spindlegear 1, and a magnetic sensor 40 are not illustrated in cross section.In FIG. 28, a state where a tab 15 a provided in the case 15 is engagedwith a recessed portion 10 aa provided in the main base 10, and a statewhere a tab 15 b provided in the case 15 is engaged with a recessedportion 10 ab provided in the main base 10, are illustrated. FIG. 29 isan exploded perspective view of the permanent magnet 8, the magnetholder 6, the layshaft gear 5, and the bearings 7 as illustrated in FIG.21. FIG. 30 is an exploded perspective view of the permanent magnet 9,the main spindle gear 1, the motor shaft 201 as illustrated in FIG. 20.

Hereinafter, the configuration of the absolute encoder 100-2 will bedescribed in detail with reference to FIGS. 13 to 30. The absoluteencoder 100-2 includes the main spindle gear 1, the intermediate gear 2,the bearing 3, the shaft 4, the layshaft gear 5, the magnet holder 6,the bearings 7, the permanent magnet 8, and the permanent magnet 9. Theabsolute encoder 100-2 includes the main base 10, the leaf spring 11,the screw 12, the substrate mounting screw 13, the screw 14, the case15, the mounting screw 16, the substrate 20. The absolute encoder 100-2includes the microcomputer 21, a bidirectional driver 22, a line driver23, a connector 24, the magnetic sensor 40, and the magnetic sensor 50.

The motor 200 may be, for example, a stepping motor, a DC brushlessmotor, or the like. For example, the motor 200 is used as a drive sourcethat drives a robot such as an industrial robot, via a decelerationmechanism such as strain wave gearing. The motor 200 includes the motorshaft 201. As illustrated in FIG. 20, one end of the motor shaft 201protrudes from the housing 202 of the motor 200 in the Z-axis positivedirection. As illustrated in FIG. 13, one end of the motor shaft 201protrudes from the housing 202 of the motor 200 in the negative Z-axisdirection. The motor shaft 201 is an example of a main shaft.

The outline shape of the motor 200 in a plan view is, for example, asquare shape. Each of four sides corresponding to the appearance of themotor 200 has a length of 25 mm. Among the four sides corresponding tothe outline of the motor 200, each of a first side and a second sideparallel to the first side is parallel to the Y-axis. Among the foursides, each of a third side adjacent to the first side and a fourth sideparallel to the third side is parallel to the X-axis. Also, the absoluteencoder 100-2 provided for the motor 200 is a 25 mm per side square,corresponding to the outline shape of the motor 200, which is a 25 mmper side square in a plan view.

Hereafter, each of the components provided in the absolute encoder 100-2will be described.

As illustrated in FIG. 20, the main spindle gear 1 is a cylindricalmember that is coaxially provided with the motor shaft 201. The mainspindle gear 1 includes a first cylindrical portion 1 a beingcylindrical, and a second cylindrical portion 1 b being cylindrical andbeing coaxially provided with the first cylindrical portion 1 a, towardthe positive Z-axis direction of the first cylindrical portion 1 a. Themain spindle gear 1 includes a communicating portion 1 c that connectsthe first cylindrical portion 1 a, which is provided inwardly in aradial direction of the second cylindrical portion 1 b, and includes thesecond cylindrical portion 1 b and a worm gear 1 d provided outwardly inthe radial direction of the second cylindrical portion 1 b. In such amanner, by forming the communicating portion 1 c, the communicatingportion 1 c serves as a path for escaping the air when the main spindlegear 1 is press-fitted into the motor shaft 201. An inner diameter ofthe communicating portion 1 c is smaller than an inner diameter of eachof the first cylindrical portion 1 a and an inner diameter of the secondcylindrical portion 1 b. A space surrounded by a bottom 1 e of thecommunicating portion 1 c, which is an end surface thereof in thenegative Z-axis direction, and an inner peripheral surface of the firstcylindrical portion 1 a, is defined as a press-fit portion if forsecuring the main spindle gear 1 to an end of the motor shaft 201. Thepress-fit portion 1 f is a recessed portion to recess the end portion ofthe first cylindrical portion 1 a, from the negative Z-axis directiontoward the positive Z-axis direction. The motor shaft 201 ispress-fitted into the press-fit portion 1 f, and the main spindle gear 1rotates integrally with the motor shaft 201. The worm gear 1 d is a gearof the main spindle gear 1.

A space surrounded by a bottom 1 g, which is an end surface of thecommunicating portion 1 c in the positive Z-axis, and an innerperipheral surface of a second cylindrical portion 1 b, is defined as amagnet holding portion 1 h for securing the permanent magnet 9. Themagnet holding portion 1 h is a recessed portion to recess the endportion of the second cylindrical portion 1 b, from the positive Z-axistoward the negative Z-axis direction. The permanent magnet 9 ispress-fitted into the magnet holding portion 1 h. The outer peripheralsurface of the permanent magnet 9 press-fitted into the magnet holdingportion 1 h contacts the inner peripheral surface of the secondcylindrical portion 1 b, and the lower surface 9 b of the permanentmagnet 9 contacts the bottom 1 g of the second cylindrical portion 1 b.In such a manner, the permanent magnet 9 is positioned in an axialdirection and is positioned in the direction perpendicular to the axialdirection. The axial direction of the permanent magnet 9 corresponds tothe central axis direction of the motor shaft 201.

As illustrated in FIGS. 16 to 18 and 20, the worm gear 1 d is composedof helically formed teeth, and engages with the worm wheel 2 a of theintermediate gear 2. The worm wheel 2 a is a gear of the intermediategear 2. In FIG. 20, illustration of the teeth shape is omitted. The wormgear 1 d is formed of, for example, a polyacetal resin. The worm gear 1d is an example of a first drive gear.

As illustrated in FIGS. 16 to 19, and the like, the intermediate gear 2is rotatably supported by the shaft 4, above the upper surface of themain base 10. The central axis of the intermediate gear 2 is parallel tothe X-Y plane. The central axis of the intermediate gear 2 is notparallel to each of the X axis and Y axis in a plan view. In otherwords, the central axis direction of the intermediate gear 2 is obliqueto an extending direction of each of the X axis and Y axis. When thecentral axis direction of the intermediate gear 2 is oblique to theextending direction of each of the X axis and Y axis, it means that thecentral axis of the intermediate gear 2 extends obliquely with respectto each of four sides of the main base 10. As illustrated in FIGS. 16and 17, the four sides of the main base 10 are composed of a first side301 parallel to the Y-Z plane, a second side 302 parallel to the firstside 301, a third side 303 that is parallel to the X-Z plane and that isadjacent to the first side 301, and a fourth side 304 parallel to thethird side 303. The first side 301 is a side of the main base 10provided toward the positive X-axis direction. The second side 302 is aside of the main base 10 provided toward the negative X-axis direction.The third side 303 is a side of the main base 10 provided toward thepositive Y-axis direction. The fourth side 304 is a side of the mainbase 10 provided toward the negative Y-axis direction.

As an example, the dimensions of the absolute encoder 100-2 in a planview are adjusted to correspond to the dimensions of the motor 200 thatis a square of 25 mm sides. In such a manner, the intermediate gear 2disposed parallel to the X-Y plane is provided so as to extend obliquelywith respect to each of the four sides of the main base 10, and thus thedimensions of the absolute encoder 100-2 can be reduced in a horizontaldirection. The horizontal direction corresponds to a directionperpendicular to the central axis of the motor shaft 201, andcorresponds to a direction parallel to the X-Y plane.

As illustrated in FIGS. 15 to 19, and the like, the intermediate gear 2includes the worm wheel 2 a, the worm gear 2 b, a shaft receivingportion 2 c, the press-fit portion 2 d, a sliding portion 2 e, a bottom2 f, and a through-hole 2 g. The intermediate gear 2 is a cylindricalmember in which the shaft 4 is inserted into the through-hole 2 g,through which the member is provided along a central axis of theintermediate gear 2. The through-hole 2 g defines a space surrounded bythe inner peripheral surface of the intermediate gear 2. Theintermediate gear 2 is a member integrally formed of metal, resin, orthe like. In this description, as an example, the intermediate gear 2 isformed of a polyacetal resin.

The worm wheel 2 a is a gear that the worm gear 1 d of the main spindlegear 1 engages with. The worm wheel 2 a is an example of a first drivengear and is a gear of the intermediate gear 2. The worm wheel 2 a isaxially provided at a location near a middle portion of the intermediategear 2, in an axial direction of the intermediate gear 2. The worm wheel2 a is configured with a plurality of teeth that are provided on theouter periphery of a given cylindrical portion of the intermediate gear2.

The outer diameter of the worm wheel 2 a is smaller than the outerdiameter of the worm gear 1 d. The central axis of the worm wheel 2 a isparallel to the top surface of the main base 10, and when the outerdiameter of the worm wheel 2 a is decreased, the size of the absoluteencoder 100-2 can be reduced in the Z-axis direction (height direction).

The worm gear 2 b is configured with helically formed teeth, and isprovided adjacently and coaxially with the worm wheel 2 a. The worm gear2 b is provided on the outer periphery of a given cylindrical portion ofthe intermediate gear 2. When the worm gear 2 b engages with the wormwheel 5 a provided in the layshaft gear 5, a rotating force of theintermediate gear 2 is transmitted to the layshaft gear 5. The worm gear2 b is an example of a second drive gear, and is a gear of theintermediate gear 2. The worm wheel 5 a is a gear of the layshaft gear5. When viewed from a direction that is both perpendicular to thecenterline of the worm wheel 5 a and perpendicular to the centerline ofthe worm gear 2 b, the centerline of the worm wheel 5 a andperpendicular to the centerline of the worm gear 2 b intersect eachother.

A smaller value for the outer diameter of the worm gear 2 b is set tothe extent possible, in order to allow for the reduced size of theabsolute encoder 100-2 in the Z-axis direction (height direction).

As illustrated in FIG. 18, the shaft receiving portion 2 c is providedon the side of the intermediate gear 2 opposite the press-fit portion 2d. That is, on the sliding portion 2 e-side of the intermediate gear 2,the shaft receiving portion 2 c is provided radially and inwardly on theinner peripheral surface of the intermediate gear 2. The shaft 4 capableof sliding is inserted through the shaft receiving portion 2 c, and theintermediate gear 2 is rotatably supported by the shaft 4.

The press-fit portion 2 d is a recessed portion inside the worm gear 2 bto recess, in the axial direction Td, an end surface of the intermediategear 2 toward a middle portion of the intermediate gear 2, andcommunicates with the through-hole 2 g. The press-fit portion 2 d can bedefined as a portion of the through-hole 2 g, where an opening diameterat an end portion of the through-hole 2 g is increased. An outer ring 3a of the bearing 3 is press-fitted into and secured to the press-fitportion 2 d.

As illustrated in FIGS. 16 to 18, FIG. 22, FIG. 23, and the like, thesliding portion 2 e of the intermediate gear 2 is provided at one end ofthe intermediate gear 2. That is, the sliding portion 2 e is providedopposite the worm gear 2 b with respect to the axial direction Td on theside of the intermediate gear 2. The sliding portion 2 e of theintermediate gear 2 contacts a sliding portion 11 a of the leaf spring11. The leaf spring 11 is an example of an elastic member and is, forexample, made of metal. The sliding portion 11 a of the leaf spring 11is configured with two bifurcated portions each of which is branchedfrom a base 11 d of the leaf spring 11. The base 11 d of the leaf spring11 is a plate-shaped member provided between a mounting portion 11 b andthe sliding portion 11 a in the entire leaf spring 11.

A space defining a greater diameter than the shaft 4 is formed betweenthe two bifurcated portions that constitute the sliding portion 11 a ofthe leaf spring 11. In such a manner, each of the two bifurcatedportions extends across the shaft 4, and the mounting portion 11 b ofthe leaf spring 11 is secured to the leaf-spring mounting surface 10 ewith the screw 12, so as not to contact the shaft 4, where theleaf-spring mounting surface 10 e is disposed on a wall 72 of the mainbase 10.

After the intermediate gear 2 is assembled, the sliding portion 11 a ofthe leaf spring 11 is disposed at a location facing the sliding portion2 e of the intermediate gear 2. The sliding portion 2 e of theintermediate gear 2 contacts the sliding portion 11 a of the leaf spring11, and when the sliding portion 2 e is pressed by the sliding portion11 a, the sliding portion 2 e is preloaded in a direction from one end 4a of the shaft 4 to the other end 4 b of the shaft 4, along the centralaxis of the shaft 4. In such a state, when the intermediate gear 2rotates, the sliding portion 2 e of the intermediate gear 2 slides,while contacting the sliding portion 11 a of the leaf spring 11.

The bottom 2 f of the intermediate gear 2 is positioned next to thepress-fit portion 2 d and contacts a side surface 3 c of the outer ring3 a of the bearing 3. The outer ring 3 a is press-fitted into thepress-fit portion 2 d until the side surface 3 c of the outer ring 3 acontacts the bottom 2 f.

The through-hole 2 g of the intermediate gear 2 passes through theintermediate gear 2 along the central axis of the intermediate gear,from the shaft receiving portion 2 c toward the press-fit portion 2 d,and is disposed coaxially with the shaft 4. The inner diameter of thethrough-hole 2 g is greater than the outer diameter of the shaft 4, andthus a given space is secured between the through-hole 2 g and the outerperipheral surface of the shaft 4.

As illustrated in FIG. 18 and FIG. 19, the bearing 3 includes the outerring 3 a, an inner ring 3 b, the side surface 3 c, and a side surface 3d. The side surface 3 c of the bearing 3 is a side surface of the outerring 3 a in the axial direction Td of the shaft 4, as represented by thearrow in FIG. 18, and the side surface 3 d of the bearing 3 is a sidesurface of the inner ring 3 b in such an axial direction. Note that inthe embodiment of the present invention, the (central) axial directionof each of the intermediate gear 2 and the shaft 4 is represented by Td.

The outer ring 3 a of the bearing 3 is press-fitted into and secured tothe press-fit portion 2 d, and the side surface 3 c contacts the bottom2 f and thus is secured. The shaft 4 is inserted into the inner ring 3b. As illustrated in FIG. 18, the side surface 3 d of the inner ring 3 bcontacts a contact surface 10 c of the wall 80 of the main base 10. Withthe contact surface 10 c, a location of the intermediate gear 2 in theaxial direction Td is determined. As described above, the intermediategear 2 is preloaded by the leaf spring 11, in the axial direction Tdfrom one end 4 a of the shaft 4 toward the other end 4 b of the shaft 4,and thus the side surface 3 c of the outer ring 3 a of the bearing 3 incontact with the bottom 2 f of the intermediate gear 2 is also preloadedin the same direction as the axial direction. Accordingly, the innerring 3 b of the bearing 3 is also preloaded in the same direction as theabove direction, so that the side surface 3 d of the inner ring 3 b ofthe bearing 3 becomes in contact with the contact surface 10 c of thewall 80. As a result, a given preloading force is transferred to thecontact surface 10 c of the wall 80, and the intermediate gear 2 isstably supported in the axial direction Td of the shaft 4. Thepreloading force will be described below in detail.

The outer ring 3 a of the bearing 3 is rotatably provided with respectto the inner ring 3 b. In such a manner, the intermediate gear 2 isrotatably supported by the shaft 4, at two locations of the shaftreceiving portion 2 c of the intermediate gear 2 and the bearing 3, asillustrated in FIG. 18. Note that the shaft 4 is formed, for example, ofstainless steel.

As illustrated in FIG. 18, each of the wall 70 and the wall 80 is anexample of a holding portion to rotatably hold the intermediate gear 2through the shaft 4. The wall 80 is integrally provided on the uppersurface of the base 60, so as to form a pair with the wall 70, andextends from the upper surface of the base 60, toward the positiveZ-axis direction. In the entire upper surface of the base 60, the wall80 is provided in a plan view, in a region that is toward the secondside 302 in the X-axis direction with respect to the middle portion ofthe base 60 and that is toward the third side 303 in the Y-axisdirection with respect to the middle portion of the base 60. In theregion described above, the wall 80 is also provided at a location nearthe second side 302 and is provided near the middle portion of the base60 in the Y-axis direction. The wall 70, the wall 80, and the shaft 4serve as a holding portion to rotatably hold the intermediate gear 2.The shaft 4 is a cylindrical member and has one end 4 a and the otherend 4 b. The other end 4 b of the shaft 4 is press-fitted into andsecured to a hole 10 b formed in the wall 80 of the main base 10. Incontrast, the one end 4 a of the shaft 4 is inserted into and positionedin a hole 10 a formed in the wall 70. It is not necessary for the oneend 4 a of the shaft 4 to be pressed-fitted into the hole 10 a. Asdescribed above, the one end 4 a of the shaft 4 is inserted into thehole 10 a without being press-fitted into the hole 10 a, therebyfacilitating assembly of the shaft 4, in comparison to a case where theone end 4 a of the shaft 4 is pressed-fitted into the hole 10 a.

As illustrated in FIG. 17 and the like, in the absolute encoder 100-2,the layshaft gear 5 is provided on the side opposite the main spindlegear 1 with respect to the intermediate gear 2. For example, thelayshaft gear 5 is disposed in a region near a given corner of the mainbase 10, in a region surrounded by the four sides of the main base 10.The given corner is, for example, a portion at which the second side 302and the third side 303, as illustrated in FIG. 17, meet. In such amanner, the layshaft gear 5 and the main spindle gear 1 utilizes alimited region of the main base 10 to be arranged in a manner ofsandwiching the intermediate gear 2. Thus, in comparison to a case wherethe layshaft gear 5 and the main spindle gear 1 are disposed adjacent toeach other without sandwiching the intermediate gear 2, a distance fromthe layshaft gear 5 to the main spindle gear 1 can be increased.

The magnetic sensor 40 detects changes in magnetic flux that is inducedthrough the permanent magnet 9 in accordance with rotation of thepermanent magnet 9, which rotates together with the main spindle gear 1.In such a manner, the magnetic sensor 40 can detect a correspondingrotation angle of the main spindle gear 1. In contrast, the magneticsensor 50 detects changes in magnetic flux that is induced through thepermanent magnet 8 in accordance with rotation of the permanent magnet8, which rotates together with the layshaft gear 5. In such a manner,the magnetic sensor 50 can detect a corresponding rotation angle of thelayshaft gear 5.

Hereafter, magnetic interference will be described, where for example,if the main spindle gear 1 and the layshaft gear 5 are disposed adjacentto each other, a portion of magnetic flux induced through each of thepermanent magnet 8 and the permanent magnet 9 might influence a magneticsensor that does not correspond to a given permanent magnet among thepermanent magnet 8 and the permanent magnet 9.

FIG. 31 is a diagram illustrating a manner of a waveform (A) of magneticflux that is from the permanent magnet 9 provided with respect to themain spindle gear 1 and that is detected by the magnetic sensor 40, awaveform (B) of magnetic flux that is from the permanent magnet 9provided with respect to the layshaft gear 5 and that is detected by themagnetic sensor 50, and a magnetically interfering waveform (C) of themagnetic flux, from the permanent magnet 9, on which a portion of themagnetic flux from the permanent magnet 8 is superimposed as leakagemagnetic flux, where the magnetically interfering waveform (c) isdetected by the magnetic sensor 40. The vertical axis represents themagnetic flux, and the horizontal axis represents the rotation angle ofthe main spindle gear 1. In such a manner, the magnetic sensor 40desirably detects the waveform (A) above. However, if magneticinterference occurs, the waveform illustrated in (C) above is produced,and thus the waveform could not be detected accurately.

Likewise, FIG. 32 is a diagram illustrating a concept of a waveform (A)of magnetic flux that is from the permanent magnet 8 provided withrespect to the layshaft gear 5 and that is detected by a magnetic sensor50, a waveform (B) of magnetic flux that is from the permanent magnet 9provided with respect to the main spindle gear 1 and that is detected bythe magnetic sensor 40, and a magnetically interfering waveform (C) ofthe magnetic flux, from the permanent magnet 8, on which a portion ofthe magnetic flux from the permanent magnet 9 is superimposed as leakagemagnetic flux, where the magnetically interfering waveform (c) isdetected by the magnetic sensor 50. The vertical axis represents themagnetic flux, and the horizontal axis represents the rotation angle ofthe layshaft gear 5. In such a manner, the magnetic sensor 50 desirablydetects the waveform (A) above. However, if magnetic interferenceoccurs, the waveform illustrated in (C) above is produced, and thus thewaveform could not be detected accurately.

Accordingly, in the absolute encoder 100-2 according to the secondembodiment, the main spindle gear 1 and the permanent magnet 9 are eachdisposed at a distance from the layshaft gear 5 and the permanent magnet8, such that the intermediate gear 2 is provided between a pair of themain spindle gear 1 and the permanent magnet 9 and a pair of thelayshaft gear 5 and the permanent magnet 8. Thus, the occurrence of themagnetic interference, in which a portion of the magnetic flux inducedthrough each of the permanent magnet 8 and the permanent magnet 9influences a given magnetic sensor that does not correspond to a givenpermanent magnet among the permanent magnet 8 and the permanent magnet9, can be reduced. For example, in the magnetic sensor 50, which isprovided for primary purposes of detecting changes in magnetic flux thatis induced through the permanent magnet 8 provided with respect to thelayshaft gear 5, interference of a portion of magnetic flux to beinduced, as leakage magnetic flux, through the permanent magnet 9provided with respect to the main spindle gear 1 can be mitigated. Also,in the magnetic sensor 40, which is provided for primary purposes ofdetecting changes in magnetic flux that is induced through the permanentmagnet 9, interference of a portion of magnetic flux to be induced, asleakage magnetic flux, through the permanent magnet 8 provided withrespect to the layshaft gear 5 can be mitigated.

As described above, in the absolute encoder 100-2 according to thesecond embodiment, decreases in accuracy of the magnetic sensor 50 todetect the rotation angle or the rotation amount of the layshaft gear 5can be prevented, as well as relatively reducing the size of theabsolute encoder 100-2 in a plan view. Further, in the absolute encoder100-2, decreases in accuracy of the magnetic sensor 40 to detect therotation angle or the rotation amount of the main spindle gear 1 can beprevented, as well as relatively reducing the size of the absoluteencoder 100-2 in a plan view.

As illustrated in FIG. 21, the layshaft gear 5 is a cylindrical memberthat is press-fitted into and secured to the shaft 6 b of the magnetholder 6. The layshaft gear 5 includes the worm wheel 5 a and athrough-hole 5 b. The layshaft gear 5 is a member integrally molded frommetal or resin. In this description, the layshaft gear 5 is formed of apolyacetal resin, as an example.

The worm wheel 5 a is a gear that engages with the worm gear 2 b. Theworm wheel 5 a is an example of a second driven gear. The worm wheel 5 ais configured with a plurality of teeth that are provided on the outerperiphery of a given cylindrical portion of the layshaft gear 5. In FIG.16, when the intermediate gear 2 rotates, a rotating force of theintermediate gear 2 is transferred to the layshaft gear 5 through theworm gear 2 b and the worm wheel 5 a.

The through-hole 5 b is a hole through the cylindrical layshaft gear 5along the central axis thereof. The shaft 6 b of the magnet holder 6 ispress-fitted into the through-hole 5 b, and the layshaft gear 5 rotatestogether with the magnet holder 6.

As illustrated in FIG. 21 and FIG. 29, the magnet holder 6 includes themagnet holding portion 6 a, the shaft 6 b, and a head 6 c. The magnetholder 6 is a member integrally molded from metal or resin. In thisdescription, the magnet holder 6 is formed of non-magnetic stainlesssteel, as an example.

Outer rings 7 a of the two bearings 7 are press-fitted into an innerperipheral surface 10 dc of the bearing holder 10 d formed in the mainbase 10. Note that each of the two bearings 7 has a given outer ring 7 aand a given inner ring 7 b.

The shaft 6 b of the magnet holder 6 is a cylindrical member and ispress-fitted into the through-hole 5 b of the layshaft gear 5. A lowerportion of the shaft 6 b is inserted into the inner rings 7 b of the twobearings 7. In such a manner, the magnet holder 6 is pivoted by the twobearings 7, with respect to the main base 10, and rotates together withthe layshaft gear 5.

The head 6 c is provided at the upper end of the magnet holder 6. Thehead 6 c is a cylindrical member with a bottom. The magnet holdingportion 6 a is formed at the head 6 c. The magnet holding portion 6 a isa recessed portion to downwardly recess the upper end surface of thehead 6 c. The outer peripheral surface of the permanent magnet 8disposed in the magnet holding portion 6 a contacts the inner peripheralsurface of the head 6 c. Thus, the permanent magnet 8 is secured to themagnet holding portion 6 a of the head 6 c.

The shaft 6 b of the magnet holder 6 is pivoted by the two bearings 7disposed at the bearing holder 10 d that is formed in the main base 10,and thus inclination of the magnet holder 6 can be prevented. In such amanner, if the two bearings 7 are disposed to the extent possible to beapart from each other in the axial direction of the shaft 6 b, effectsof preventing the inclination of the magnet holder 6 are obtained.

As illustrated in FIG. 21, an upper portion 10 db of the bearing holder10 d is in an upper-side region of the bearing holder 10 d in the Z-axisdirection, in the entire bearing holder 10 d. One bearing 7 is providedinside an upper portion 10 db of the bearing holder 10 d. A lowerportion 10 da of the bearing holder 10 d is in a lower-side region ofthe bearing holder 10 d in the Z-axis direction, in the entire bearingholder 10 d. Another bearing 7 is provided inside the lower portion 10da of the bearing holder 10 d.

As illustrated in FIG. 21, a cut-out portion 202 a is provided in aportion of the housing 202 of the motor 200. The cut-out portion 202 ais a recessed portion recessed toward the negative Z-axis direction. Thelower portion 10 da of the bearing holder 10 d is provided to protrude,in the main base 10. In such a manner, by providing the cut-out portion202 a in the housing 202 of the motor 200, interference of the bearingholder 10 d with the motor 200 is avoided. The lower portion 10 da ofthe bearing holder 10 d is in the lower-side region of the bearingholder 10 d in the Z-axis direction, in the entire bearing holder 10 d.The one bearing 7 is provided inside the lower portion 10 da of thebearing holder 10 d. In such a manner, by providing the cut-out portion202 a in the housing 202 of the motor 200, a longer distance between thetwo bearings 7 to be separated in the Z-axis direction can be set incomparison to a case where the cut-out portion 202 a is not provided.The upper portion 10 db of the bearing holder 10 d is in the upper-sideregion of the bearing holder 10 d in the Z-axis direction, in the entirebearing holder 10 d.

When each bearing 7 is disposed in the axial direction of the shaft 6 bof the magnet holder 6, at a location closer to the magnet holdingportion 6 a and the permanent magnet 8, shaft deflection can be reducedduring rotation of the magnet holder 6 and the permanent magnet 8.Further, the outer diameter side of the upper portion 10 db of thebearing holder 10 d is proximal to the intermediate gear 2. Thus, when aslope is formed on the upper portion 10 db of the bearing holder 10 d,interference with an addendum circle of the intermediate gear 2 isavoided, while each bearing 7 can be provided at a location closer tothe magnet holding portion 6 a and the permanent magnet 8.

By detecting changes in magnetic flux that is induced through thepermanent magnet 9 in accordance with rotation of the permanent magnet9, which rotates together with the main spindle gear 1, the magneticsensor 40 can detect a corresponding rotation angle of the main spindlegear 1. By detecting changes in magnetic flux that is induced throughthe permanent magnet 8 in accordance with rotation of the permanentmagnet 8, which rotates together with the layshaft gear 5, the magneticsensor 50 can detect a corresponding rotation angle of the layshaft gear5.

As illustrated in FIG. 21 and FIG. 29, the permanent magnet 8 has asurface 8 a. The permanent magnet 8 is approximately cylindrical, and acentral axis MC1 (an axis representing the center of the permanentmagnet 8, or an axis through the center of an interface between magneticpoles) of the permanent magnet 8 coincides with each of a central axisHC1 of the magnet holder 6, a central axis GC1 of the layshaft gear 5,and a central axis BC of the bearing 7. The surface 8 a of the permanentmagnet 8 faces the surface 50 a of the magnetic sensor 50, at a fixeddistance from the surface 50 a of the magnetic sensor 50. By matchingthe central axes in such a manner, a given rotation angle or rotationamount can be detected with higher accuracy.

Note that in the present embodiment, as illustrated in FIG. 29, twomagnetic poles (N/S) of the permanent magnet 8 are formed adjacent toeach other at a plane (X-Y plane) perpendicular to the central axis MC1of the permanent magnet 8. In other words, in the central axis MC1, thecenter of rotation of the permanent magnet 8 desirably coincides withthe center of the interface between the magnetic poles. Thus, accuracyfor detecting a given rotation angle or rotation amount can be furtherimproved.

As illustrated in FIG. 20 and FIG. 30, the permanent magnet 9 is aapproximately cylindrical permanent magnet that is press-fitted into themagnet holding portion 1 h of the main spindle gear 1, and has the uppersurface 9 a and a lower surface 9 b. The upper surface 9 a of the magnetfaces a surface 40 a of the magnetic sensor 40, at a fixed distance fromthe surface 40 a of the magnetic sensor 40. The lower surface 9 b of themagnet contacts the bottom 1 g of the magnet holding portion 1 h of themain spindle gear 1, and with the lower surface 9 b of the magnet, alocation (location in the Z-axis direction) of the main spindle gear 1in a central axis GC2-direction is determined. The central axis MC2 (anaxis representing the center of the permanent magnet 9 or an axisthrough the center of an interface between magnetic poles) of thepermanent magnet 9 coincides with each of the central axis GC2 of themain spindle gear 1 and a central axis RC of the motor shaft 201. Bymatching the central axes in such a manner, the rotation angle orrotation amount can be detected with higher accuracy.

Note that in the present embodiment, as illustrated in FIG. 30, it isdesirable that the two magnetic poles (N/S) of the permanent magnet 9are formed adjacent to each other in a plane (X-Y plane) perpendicularto the central axis MC2 of the permanent magnet 9. Thus, accuracy indetecting a given rotation angle or rotation amount is furtherincreased.

Note that each of the permanent magnet 8 and the permanent magnet 9 isformed of a magnetic material such as a ferrite-type or Nd(neodymium)-Fe (iron)-B (boron). Each of the permanent magnet 8 and thepermanent magnet 9 may be, for example, a rubber magnet including aresin binder, a bond magnet, or the like.

In FIG. 25, a positioning hole 20 a, a positioning hole 20 b, a hole 20c, a hole 20 d, and a hole 20 e, which are multiple through-holes formedin the substrate 20, are illustrated. The shape of a wall surfaceforming the positioning hole 20 a is a circle, for example. The shape ofa wall surface forming the positioning hole 20 b is an ellipse, forexample. Each of the hole 20 c, the hole 20 d, and the hole 20 e is athrough-hole for securing the substrate 20 to the main base 10 with thesubstrate-mounting screws 13, as illustrated in FIG. 14. The shape ofthe wall surface forming each of the hole 20 c, the hole 20 d, and thehole 20 e is a circle, for example. The diameter of the wall surfaceforming each of the hole 20 c, the hole 20 d, and the hole 20 e isgreater than a diameter of an external thread of each substrate-mountingscrew 13 and is smaller than a diameter of a head of eachsubstrate-mounting screw 13.

As illustrated in FIG. 15 to FIG. 18, FIG. 22 to FIG. 24, and the like,the main base 10 includes the hole 10 a, the hole 10 b, the contactsurface 10 c, the bearing holder 10 d, a leaf-spring mounting surface 10e, the base 60, the wall 70, the wall 80, an opening 10-1, and a screwhole 10 f. The main base 10 includes the substrate positioning pin 10 g,the substrate positioning pin 10 j, a distal end 10 h, a distal end 10k, a pillar 10 m, a pillar 10 q, a pillar 10 s, a screw hole 10 u, ascrew hole 10 v, and a screw hole 10 w. The substrate positioning pin 10g, the substrate positioning pin 10 j, the pillar 10 m, the pillar 10 q,and the pillar 10 s are examples of pillar members. A stepped portion 10i is formed between the distal end 10 h of the substrate positioning pin10 g, which extends in the Z-axis direction from the main base 10, and abase 10 gl of the substrate positioning pin 10 g. When the distal end 10h of the substrate positioning pin 10 g is inserted into the positioninghole 20 a formed in the substrate 20, a space is formed between thelower surface 20-1 of the substrate 20 and the stepped portion 10 i.Likewise, a stepped portion 101 is formed between the distal end 10 k ofthe substrate positioning pin 10 j, which extends in the Z-axisdirection from the main base 10, and a base 10 jl of the substratepositioning pin 10 j. When the distal end 10 k of the substratepositioning pin 10 j is inserted into the positioning hole 20 b formedin the substrate 20, a space is formed between the lower surface 20-1 ofthe substrate 20 and the stepped portion 101. In such a manner, when thetwo substrate positioning pins 10 g and 10 j are used, the location ofthe substrate 20 in the direction perpendicular to the Z-axis directionis determined. However, because a given space is formed between each ofthe stepped portion 10 i and the stepped portion 101, and the substrate20, the location of the substrate 20 in the Z-axis direction is notdetermined by the two substrate positioning pins 10 g and 10 j.

The base 60 of the main base 10 is, for example, an integrally moldedaluminum die cast member, and is a plate-like member that isapproximately square in a plan view. The base 60 is an example of aplate. The base 60 is mounted on the upper surface of the motor 200.

The opening 10-1 illustrated in FIG. 15 passes through the base 60 in athickness direction (Z-axis direction). The main spindle gear 1 isinserted through the opening 10-1. The opening 10-1 is an example of afirst through-hole.

As illustrated in FIG. 16, FIG. 17, FIG. 22, FIG. 23, and the like, thewall 70 has a wall 71 and a wall 72. The wall 70 serves to support theshaft 4 and secure the leaf spring 11. The wall 71 is integrallyprovided on the upper surface of the base 60 and extends in the positiveZ-axis direction from the base 60. The wall 70 is provided in a planview in a region that is toward the first side 301 with respect to themiddle portion of the base 60 in the X-axis direction and that is towardthe fourth side 304 with respect to the middle portion of the base 60 inthe Y-axis direction, in the entire upper surface of the base 60. Thewall 71 has a mounting surface 10 ad positioned toward the positiveX-axis direction, and has a screw hole 10 ae through the wall 71 in thepositive X-axis direction. As illustrated in FIG. 13, FIG. 26, and FIG.27, the mounted screw 16 is inserted through a hole 15 d of the case 15to be screwed into the screw hole 10 ae. Thus, the inner surface of thecase 15 is secured by contact with the mounting surface 10 ad of thewall 71.

As illustrated in FIG. 17, the wall 72 is provided in a plan view, in aregion that is toward the first side 301 with respect to the middleportion of the base 60 in the X-axis direction and that is toward thethird side 303 with respect to the middle portion of the base 60 in theY-axis direction, in the entire upper surface of the base 60. The wall72 is connected to the wall 71 and extends from the wall 71 toward theproximity of the middle portion of the third side 303. An end portion ofthe wall 72 toward the third side 303 is connected to the pillar 10 s.The pillar 10 s connected to the wall 72 is provided at a location nearthe middle portion of the main base 10 in the X-axis direction, as wellas being situated at a location near the third side 303 of the main base10. In such a manner, the wall 72 extends from the wall 71 toward thepillar 10 s. In other words, the wall 72 extends obliquely with respectto each of the X-axis and Y-axis, in a plan view.

As illustrated in FIG. 23, the screw 12 is inserted through a hole 11 cformed in the mounting portion 11 b of the leaf spring 11, and isscrewed into a screw hole 10 f formed in the wall 72 of the main base10. In such a manner, the mounting portion 11 b of the leaf spring 11contacts the leaf-spring mounting surface 10 e formed in the wall 72,and the leaf spring 11 is thereby secured to the wall 72. The wall 72serves as a securing portion for the leaf spring 11 to be secured. Atthis time, as illustrated in FIG. 17 and FIG. 18, the sliding portion 11a of the leaf spring 11 contacts the sliding portion 2 e of theintermediate gear 2 into which the shaft 4 is inserted.

A mounting angle θ illustrated in FIG. 18 will be described. The wormgear 1 d of the main spindle gear 1 is engaged with the worm wheel 2 a,and in accordance with rotation of the worm gear 1 d of the main spindlegear 1, a first thrust force against the intermediate gear 2 isgenerated in the direction from the other end 4 b of the shaft 4 to oneend 4 a of the shaft 4, or the direction from one end 4 a of the shaft 4to the other end 4 b of the shaft 4. Further, by engagement of the wormgear 2 b with the worm wheel 5 a of the layshaft gear 5, a second thrustforce against the intermediate gear 2 is also generated in the directionfrom the other end 4 b of the shaft 4 toward one end 4 a of the shaft 4,or the direction from one end 4 a of the shaft 4 toward the other end 4b of the shaft 4. In such a manner, even when the first thrust force andthe second thrust force are generated, in order to accurately transmit arotation amount of the worm gear 1 d of the main spindle gear 1 to theworm wheel 5 a of the layshaft gear 5, movement of the intermediate gear2 in the axial direction Td of the shaft 4 needs to be restricted. Theleaf spring 11 applies a preloading force to the intermediate gear 2, inthe direction from one end 4 a of the shaft 4 toward the other end 4 bof the shaft 4. A greater preloading force applied by the leaf spring 11is set in comparison to the sum of the first thrust force and secondthrust force in the direction from the other end 4 b of the shaft 4toward one end 4 a of the shaft 4.

In FIG. 18, in a state where the intermediate gear 2 is not insertedinto the shaft 4, the mounting angle θ is the same as an angle betweenthe base 11 d of the leaf spring 11, which is secured to the wall 72 ofthe main base 10, and the side surface 73 of the wall 72 that is towardthe intermediate gear 2 and that is among surfaces of the wall 72, wherethe hole 10 a through which the one end 4 a of the shaft 4 is insertedis formed at the surfaces of the wall 72. Note that the side surface 73and the shaft 4 according to the present embodiment are set at a rightangle, but may not be limited to the example described above. When theintermediate gear 2 is incorporated into the shaft 4, the slidingportion 11 a of the leaf spring 11 comes into contact with the slidingportion 2 e of the intermediate gear 2, and thus the leaf spring 11 isdeflected at a predetermined amount. In such a manner, the mountingangle θ is set to be an angle that causes a force to preload theintermediate gear 2 to be appropriately applied in the axial directionTd of the shaft 4. Thus, the leaf spring 11 preloads the intermediategear 2 in a given direction from the one end 4 a of the shaft 4 to theother end 4 b of the shaft 4. Accordingly, movement of the intermediategear 2 due to a total force for the first thrust force and the secondthrust force in the direction from the other end 4 b of the shaft 4 tothe one end 4 a of the shaft 4 can be restricted. As a result, decreasesin rotation accuracy of the layshaft gear 5 can be avoided. Note thatthe increased preloading force results in an increase in slidingresistance while the intermediate gear 2 illustrated in FIG. 18 isrotating. For this reason, the mounting angle θ is desirably set to anappropriate value that causes a sufficient preloading force allowingrestriction of the movement of the intermediate gear 2 through a giventhrust force, as well as minimizing the sliding resistance duringrotation of the intermediate gear 2. In order to set the mounting angleθ to such an appropriate value, it is necessary to increase surfaceaccuracy of the leaf-spring mounting surface 10 e on which the leafspring 11 is mounted, and to reduce an error of the mounting angle ofthe base 60 relative to the wall 70.

In the absolute encoder 100-2 according to the second embodiment, themain base 10 is formed from die-cast aluminum, and for example, asmaller error margin of the mounting angle of the wall 70 relative tothe base 60 can be set in comparison to a case where an individuallyfabricated base 60 and the wall 70 are combined with each other by sheetmetal. Thus, surface accuracy of the leaf-spring mounting surface 10 ecan be increased. As a result, the error margin of the mounting angle θof the wall 72 relative to the leaf spring 11 is decreased and thus thecontrol of the preloading force is facilitated.

As illustrated in FIG. 22, the main base 10 is secured with three screws14 that are inserted through three holes formed in the main base 10 andthat are screwed into screw holes formed in the motor 200. A screw hole10 v, a screw hole 10 u, and a screw hole 10 w are respectively formedin the positive Z-axis direction, on tip sides of the pillar 10 q, thepillar 10 m, and the pillar 10 s each of which extends from the mainbase 10 in the positive Z-axis direction. The respective substratemounting screws 13 inserted into the hole 20 c, the hole 20 e, and thehole 20 d in the substrate 20, as illustrated in FIG. 14, are screwedinto the screw hole 10 v, the screw hole 10 u, and the screw hole 10 w.In such a manner, an upper end surface 10 r of the pillar 10 q, an upperend surface 10 p of the pillar 10 m, and an upper end surface 10 t ofthe pillar 10 s contact the lower surface 20-1 of the substrate 20 asillustrated in FIG. 24. The lower surface 20-1 of the substrate 20 is asurface that faces the main base 10 and that is among two substratesurfaces of the substrate 20 in the Z-axis direction. As a result, thelocation of the substrate 20 in the Z-axis direction is determined.

As illustrated in FIG. 13, FIG. 26 to FIG. 28, and the like, the case 15has a top portion 15-1, a first side portion 15A, a second side portion15B, a third side portion 15C, and a fourth side portion 15D, and is abox-shaped member of which one side is open. For example, the case 15 ismade of resin and is a integrally molded member. The top portion 15-1corresponds to a bottom of a given box-shaped member. The top portion15-1 has a surface facing the upper surface 20-2 of the substrate 20illustrated in FIG. 14. The upper surface 20-2 of the substrate 20 is asubstrate surface opposite the lower surface 20-1 of the substrate 20.The first side portion 15A is a plate-shaped member extending from agiven side of the top portion 15-1 in the positive X-axis direction,toward the negative Z-axis direction. The second side portion 15B is aplate-shaped member extending from a given side of the top portion 15-1in the negative X-axis direction, toward the negative Z-axis direction.The third side portion 15C is a plate-shaped member extending from agiven side of the top portion 15-1 in the negative Y-axis direction,toward the negative Z-axis direction. The fourth side portion 15D is aplate-shaped member extending from a given side of the top portion 15-1in the positive Y-axis direction, toward the negative Z-axis direction.The shape of the case 15 in a plan view is a rectangular shapecorresponding to the shape of the motor 200 in a plan view. A pluralityof components provided in the absolute encoder 100-2 are accommodated ina given space in the case 15.

As illustrated in FIG. 27, the case 15 includes a tab 15 a, a tab 15 b,a tab 15 c, a hole 15 d, a recessed portion 15 e, a recessed portion 15f, a recessed portion 15 g, a connector case 15 h, and an opening 15 i.The tab 15 a is provided near an end portion of the fourth side portion15D in the negative Z-axis direction. The tab 15 a extends from thefourth side portion 15D toward the negative Y-axis direction so as toface the third side portion 15C. The tab 15 a is engaged with therecessed portion 10 aa provided in the main base 10, as illustrated inFIG. 26. The tab 15 b is provided near an end portion of the third sideportion 15C in the negative Z-axis direction. The tab 15 b extends fromthe third side portion 15C toward the positive Y-axis direction so as toface the fourth side portion 15D. The tab 15 b is engaged with arecessed portion 10 ab provided in the main base 10, as illustrated inFIG. 26. The tab 15 c is provided near an end portion of the second sideportion 15B in the negative Z-axis direction. The tab 15 c extends fromthe second side portion 15B toward the negative X-axis direction so asto face the first side portion 15A. The tab 15 c is engaged with arecessed portion 10 ac provided in the main base 10, as illustrated inFIG. 26.

The recessed portion 15 e, the recessed portion 15 f, and the recessedportion 15 g, as illustrated in FIG. 27, are recessed portions each ofwhich recesses a portion of a top 5-1 of the case 15 toward the positiveZ-axis direction, in order to avoid interference with a head of a givensubstrate mounting screw among the three substrate mounting screws 13illustrated in FIG. 14.

The connector case 15 h is a recessed portion to recess a portion of thetop 5-1 of the case 15 toward the positive Z-axis direction, in order tocover the connector 24 illustrated in FIG. 14. The bottom shape of theconnector case 15 h is rectangular in a plan view. The connector case 15h is provided in a given region that is toward the first side portion15A with respect to a middle portion of the top 15-1 in the X-axisdirection and that is proximal to the middle portion of the top 15-1 inthe Y-axis direction, in the top 15-1 of the case. The connector case 15h is provided at a portion near the first side portion 15A, in the givenregion described above.

The opening 15 i is formed between the bottom of the connector case 15 hand the first side portion 15A. The connector 24 illustrated in FIG. 14is disposed so as to face the bottom of the connector case 15 h. Theconnector 24 is, for example, an internal connector, and an externalconnector provided for one end of an external wire is inserted into theconnector 24. The external connector is inserted into the connector 24disposed in the connector case 15 h, through the opening 15 iillustrated in FIG. 27. In such a manner, a conductive terminal of theinternal connector provided for one end of the external wire iselectrically connected to a conductive terminal provided at theconnector 24. As a result, an external device connected to the other endof the external wire, and the connector 24 are electrically connectedtogether and thus signals can be transmitted between the absoluteencoder 100-2 and the external device.

Further, the connector case 15 h is provided at a location near thefirst side portion 15A, and the location of the connector 24 in a planview corresponds to the location of a connector 400 set when the motor200 is viewed from a given plane, as illustrated in FIG. 14. Byconfiguring the absolute encoder 100-2 in such a manner, a drawnlocation of the external wire to be electrically connected to a givenconductive pin provided at the connector 24 can become closer to a drawnlocation of the external wire to be electrically connected to a givenconductive pin provided at the connector 400. Thus, these external wirescan be bundled together near each of the absolute encoder 100-2 and themotor 200, thereby causing the resulting bundled wires to be easilydrawn to a given external device.

As illustrated in FIG. 25, the magnetic sensor 40, the magnetic sensor50, a microcomputer 21, a bidirectional driver 22, and a line driver 23are provided on the lower surface 20-1 of the substrate 20. The lowersurface 20-1 of the substrate 20 is a mounting surface for the magneticsensor 40 and the magnetic sensor 50. As described above, the lowersurface 20-1 of the substrate 20 contacts an upper end surface 10 r ofthe pillar 10 q, an upper end surface 10 p of the pillar 10 m, and anupper end surface 10 t of the pillar 10 s. As illustrated in FIG. 16,the pillar 10 q, the pillar 10 m, and the pillar 10 s are provided onthe main base 10 such that a difference in a separation distance betweengiven pillars is decreased when the main base 10 is viewed from a givenplane. For example, the pillar 10 q is provided near the second side302, in the proximity of the middle portion of the main base 10 in theY-axis direction. The pillar 10 q is integral with the wall 80. Thepillar 10 m is provided near a corner at which the first side 301 andthe fourth side 304 meet. The pillar 10 s is provided near the thirdside 303 in the proximity of the middle portion of the main base 10 inthe X-axis direction. The pillar 10 s is integrated with the wall 70 andthe substrate positioning pin 10 g. In such a manner, by providing thepillar 10 q, the pillar 10 m, and the pillar 10 s, the locations, in theZ-axis direction, of the magnetic sensor 40 and the magnetic sensor 50provided on the substrate 20 can be determined accurately. Note thatwhen the pillar 10 q, the pillar 10 m, and the pillar 10 s are eachformed in the X-Y plane direction at a location of the main base 10 tothe extent possible to be away from other pillars, the location of thesubstrate 20 can be maintained more stably.

In the absolute encoder 100-2 according to the second embodiment, themain base 10 is formed by die-casting. In such a manner, positionalaccuracy between given components is improved in comparison to a casewhere the base 60 of the main base 10 is fabricated by, for example,sheet metal, and then, the pillar 10 q, the pillar 10 m, the pillar 10s, the substrate positioning pin 10 g, the substrate positioning pin 10j, the wall 70, the wall 80, and the like are individually fabricated tosubsequently assemble such components. Further, the number of componentsto be used during manufacture is reduced, and thus the structure of theabsolute encoder 100-2 can be simplified. Moreover, a manufacturing timecan be reduced due to ease of assembly, thereby allowing for increasedreliability of the absolute encoder 100-2.

The magnetic sensor 40 is an example of a main spindle angular sensor.The magnetic sensor 40 is positioned directly above the permanent magnet9, at a predetermined distance from the permanent magnet 9. By detectingchanges in magnetic flux induced through the permanent magnet 9 inaccordance with rotation of the permanent magnet 9, which rotatestogether with the main spindle gear 1, the magnetic sensor 40 detectsand determines a corresponding rotation angle of the main spindle gear1, and then outputs, as a digital signal, angle information indicatingthe determined rotation angle.

The magnetic sensor 50 is an example of an angular sensor. The layshaftgear 5 is a rotating body that rotates in accordance with rotation ofthe worm wheel 5 a, which is a second driven gear. The magnetic sensor50 is positioned directly above the permanent magnet 8, at apredetermined distance from the permanent magnet 8. By detecting changesin magnetic flux induced through the permanent magnet 8 in accordancewith rotation of the permanent magnet 8, which rotates together with thelayshaft gear 5, the magnetic sensor 50 detects and determines a givenrotation angle of the layshaft gear 5, and then outputs, as a digitalsignal, angle information indicating the determined rotation angle.

For example, each of the magnetic sensor 40 and the magnetic sensor 50includes a sensing element to detect changes in magnetic flux, and anarithmetic circuit to output a digital signal indicating a rotationangle, based on the output of the sensing element. The example of thesensing element may be a combination of elements for sensing a magneticfield, such as a Hall element and a giant magneto resistive (GMR)element. The number of elements for sensing a magnetic field is, forexample, four.

When the number of threads of the worm gear 1 d of the main spindle gear1 is 4, and the number of teeth of the worm wheel 2 a of theintermediate gear 2 is 20, a deceleration ratio is 5. That is, when themain spindle gear 1 rotates 5 revolutions, the intermediate gear 2rotates one revolution. When the number of threads of the worm gear 2 bof the intermediate gear 2 is 1, and the number of teeth of the wormwheel 5 a of the layshaft gear 5 is 18, a deceleration ratio is 18. Thatis, when the intermediate gear 2 rotates 18 revolutions, the layshaftgear 5 rotates one revolution. In such a manner, when the main spindlegear 1 rotates 90 revolutions, the intermediate gear 2 rotates 18revolutions, which is given by 90÷5, and the layshaft gear 5 rotates onerevolution, which is given by 18÷18.

The permanent magnets 9 and 8 are respectively provided with respect tothe main spindle gear 1 and the layshaft gear 5 each of which rotatestogether with a given permanent magnet among the permanent magnets 9 and8. In such a manner, each of the magnetic sensor 40 and the magneticsensor 50, corresponding to a given gear, detects a given rotation angleof the given gear among the main spindle gear 1 and the layshaft gear 5,and a rotation amount of the motor shaft 201 can be thereby determined.When the main spindle gear 1 rotates one revolution, the layshaft gear 5rotates one ninetieth of one revolution, that is, at 4 degrees. In thiscase, when the rotation angle of the layshaft gear 5 is less than 4degrees, a rotation amount of the main spindle gear 1 is less than onerevolution, and when the rotation angle of the layshaft gear 5 is 4degrees or more and is less than 8 degrees, the rotation amount of themain spindle gear 1 is one revolution or more and is less than 2revolutions. In such a manner, the absolute encoder 100-2 can determinea rotation speed of the main spindle gear 1 in accordance with therotation angle of the layshaft gear 5. In particular, the absoluteencoder 100-2 can utilize a reduction ratio between the worm gear 1 dand the worm wheel 2 a, as well as a reduction ratio between the wormgear 2 b and the worm wheel 5 a, to determine the rotation speed of themain spindle gear 1 even when the rotation speed of the main spindlegear 1 is defined by a plurality of revolutions.

The microcomputer 21, the bidirectional driver 22, the line driver 23,and the connector 24 are mounted on the substrate 20. The microcomputer21, the bidirectional driver 22, the line driver 23, and the connector24 are electrically connected together by pattern wiring on thesubstrate 20.

The microcomputer 21 is configured by a central processing unit (CPU),acquires a digital signal indicating a given rotation angle to be outputfrom each of the magnetic sensor 40 and the magnetic sensor 50, andcalculates a given rotation amount of the main spindle gear 1.

The bidirectional driver 22 performs bidirectional communication with anexternal device to be connected to the connector 24. The bidirectionaldriver 22 converts data such as an operation signal, into a differentialsignal to thereby perform communication with the external device. Theline driver 23 converts data indicating a given rotational amount into adifferential signal, and outputs the differential signal in real time tothe external device connected to the connector 24. A given connector ofthe external device is connected to the connector 24. FIG. 33 is adiagram illustrating a functional configuration of the microcomputer 21provided in the absolute encoder 100-2 according to the secondembodiment of the present invention. Each block of the microcomputer 21illustrated in FIG. 33 represents a function implemented when the CPU asthe microcomputer 21 executes a program.

The microcomputer 21 includes a rotation-angle acquiring unit 21 p, arotation-angle acquiring unit 21 q, a table processing unit 21 b, arotation-amount determining unit 21 c, and an output unit 21 e. Therotation-angle acquiring unit 21 q acquires a rotation angle Aq of themain spindle gear 1 based on a signal output from the magnetic sensor40. The rotation angle Aq corresponds to angle information indicating agiven rotation angle of the main spindle gear 1. The rotation-angleacquiring unit 21 p acquires a rotation angle Ap of the layshaft gear 5based on a signal output from the magnetic sensor 50. The rotation angleAp corresponds to angle information indicating a given rotation angle ofthe layshaft gear 5. The table processing unit 21 b determines arotation speed of the main spindle gear 1 corresponding to the acquiredrotation angle Ap, with reference to a relationship table that storesthe rotation angle Ap and the rotation speed of the main spindle gear 1associated with the rotation angle Ap. The rotation-amount determiningunit 21 c determines a rotation amount corresponding to a plurality ofrevolutions of the main spindle gear 1, based on the rotation speed ofthe main spindle gear 1 determined by the table processing unit 21 b, aswell as on the acquired rotation angle Aq. The output unit 21 e convertsthe determined rotation amount corresponding to the plurality ofrevolutions of the main spindle gear 1, into information indicating thedetermined rotation amount, and outputs the information.

As described above, in the absolute encoder 100-2 according to thesecond embodiment, the layshaft gear 5 is provided on the side oppositethe main spindle gear 1 with respect to the intermediate gear 2, asillustrated in FIG. 17 and the like, and thus occurrence of magneticinterference to influence a given magnetic sensor not corresponding to agiven permanent magnet among the permanent magnet 8 and the permanentmagnet 9 can be reduced. In such a manner, by employing a structurecapable of reducing the occurrence of the magnetic interference, arelatively reduced size of the absolute encoder 100-2 can be set whenthe absolute encoder 100-2 is viewed from a plane. Accordingly, the sizeof the absolute encoder 100-2 is reduced, as well as allowing forprevention of decreases in accuracy of each of the magnetic sensor 40and the magnetic sensor 50 to detect magnetic flux.

Further, in the absolute encoder 100-2 according to the secondembodiment, the intermediate gear 2 disposed parallel to the uppersurface of the main base 10 extends obliquely with respect to each ofthe four sides of the main base 10, and further, the main spindle gear 1and the layshaft gear 5 are disposed on opposed sides with respect tothe intermediate gear 2. In such a manner, the main spindle gear 1, theintermediate gear 2, and the layshaft gear 5 can be disposed in a smallregion being a portion of the entire region of the upper surface of themain base 10, thereby reducing the dimensions of the absolute encoder100-2 with respect to the horizontal direction.

Further, in the absolute encoder 100-2 according to the secondembodiment, the outer diameter of the worm wheel 2 a and the outerdiameter of the worm gear 2 b are each set to a value to the minimumextent possible. Thus, the dimension of the absolute encoder 100-2 withrespect to the Z-axis direction (height direction) can be reduced.

As described above, the absolute encoder 100-2 according to the secondembodiment has the effect of reducing the dimension with respect to theZ-axis direction, as well as the dimensions with respect to thedirections perpendicular to the Z-axis direction, while preventing thedecrease in detection accuracy of a given rotation amount of the mainspindle gear 1.

Moreover, in the absolute encoder 100-2 according to the secondembodiment, the intermediate gear 2 is pivoted with respect to the shaft4 that is secured to the wall 80 and that is inserted into the wall 72.In other words, the intermediate gear 2 is rotatably supported withrespect to the shaft 4. However, as long as the intermediate gear 2 canbe pivoted, a method of supporting the intermediate gear 2 is notlimited to the example described above.

For example, the absolute encoder 100-2 is configured such that one end4 a of the shaft 4 is inserted into the hole 10 a formed in the wall 72and the other end 4 b of the shaft 4 is press-fitted into the hole 10 bformed in the wall 80. Further, the absolute encoder 100-2 may beconfigured such that the outer ring 3 a of the bearing 3 is press-fittedinto and secured to the press-fit portion 2 d formed in the intermediategear 2 and the shaft 4 is press fitted into and secured to the innerring 3 b of the bearing 3. In such a manner, the movement of theintermediate gear 2 secured to the shaft 4 in the axial direction Td isrestricted. Even when the absolute encoder 100-2 is configured asdescribed above, the intermediate gear 2 is rotatably supported by theshaft 4. Further, the wall 72 and the wall 80 restrict the movement ofthe shaft 4 in the axial direction Td, and the inner ring 3 b of thebearing 3 secured to the shaft 4 also restricts the movement of theintermediate gear 2 in the axial direction Td. Accordingly, the use ofthe leaf spring 11 is not applied.

Alternatively, for example, without using the bearing 3 illustrated inFIG. 18, the absolute encoder 100-2 may be configured such that in asecured state of the intermediate gear 2 to the shaft 4, the shaft 4 isrotatably supported by a bearing not illustrated, where the bearing isprovided with respect to at least one among the wall 72 and the wall 80.

When an outer ring of a given bearing not illustrated is secured to thewall 72 or the wall 80, and one end 4 a or the other end 4 b of theshaft 4 is inserted into an inner ring of the given bearing, theintermediate gear 2 is secured to the shaft 4 and the shaft 4 is pivotedby the given bearing not illustrated. Thus, the shaft 4 and theintermediate gear 2 can rotate together. In this case, the shaft 4 isnot secured to the inner ring of the bearing and is only inserted intothe inner ring thereof, and thus the shaft 4 can be moved in the axialdirection Td, together with the intermediate gear 2. Accordingly, theleaf spring 11 needs to preload the intermediate gear 2 in the axialdirection Td to thereby determine a given location of the intermediategear 2.

Alternatively, the outer ring of a given bearing not illustrated issecured to the wall 72 or the wall 80, and one end 4 a or the other end4 b of shaft 4 may be press-fitted into the inner ring of the givenbearing not illustrated. At this time, the movement of the intermediategear 2 secured to the shaft 4 is restricted in the axial direction Td.In such a manner, the intermediate gear 2 secured to the shaft 4 is onlysupported rotatably by the given bearing not illustrated, and themovement of the shaft 4 in the axial direction Td is restricted. Thus,the movement of the intermediate gear 2 in the axial direction Td isrestricted. Accordingly, the use of the leaf spring 11 is not applied.

As illustrated in FIG. 20, the magnetic sensor 40 primarily detectschanges in magnetic flux from the permanent magnet 9 that rotatestogether with the main spindle gear 1, and detects and identifies arotation angle of the main spindle gear 1. As illustrated in FIG. 21,the magnetic sensor 50 detects changes in magnetic flux from thepermanent magnet 8 that rotates together with the layshaft gear 5, anddetects and identifies a rotation angle of the layshaft gear 5. For theabsolute encoder 100-2 according to the second embodiment, as describedabove, by employing a structure that can reduce the occurrence ofmagnetic interference, the effect of magnetic flux, from the permanentmagnet 8, on the magnetic sensor 40 can be reduced. Further, the effectof magnetic flux, from the permanent magnet 9, on the magnetic sensor 50can be reduced. That is, reductions in accuracy in detecting rotationdue to magnetic interference between the main spindle gear 1 and thelayshaft gear 5 can be prevented.

As illustrated in FIG. 13, a state where the absolute encoder 100-2 isattached to the motor 200 is illustrated, and one or more permanentmagnets and one or more driving coils are provided in an interior of themotor 200. Thus, in the motor 200, magnetic flux is generated even whenthe motor shaft 201 is not rotating. Further, when a drive signal isexternally provided to the motor 200, and the motor shaft 201 is therebyrotated, magnetic flux generated is further increased. The magnetic fluxgenerated from the motor 200 may negatively influence the magneticsensor 40 and the magnetic sensor 50 that are provided inside theabsolute encoder 100-2, which might result in reductions in detectionaccuracy. When the effect of unwanted magnetic flux from the motor 200is obtained, in a case where the main base 10 is made of a ferromagneticmaterial such as iron, the effect of the magnetic flux from the motor200 can be reduced.

As described above, the absolute encoder 100-2 according to the secondembodiment includes a first worm speed-changing mechanism that includesthe worm gear 1 d of the main spindle gear 1 and the worm wheel 2 a ofthe intermediate gear 2, and includes a second worm speed-changingmechanism that includes the worm gear 2 b of the intermediate gear 2 andthe worm wheel 5 a of the layshaft gear 5. For example, a pitch circleof the worm gear 1 d is greater than a pitch circle of the worm wheel 2a, in order to make the absolute encoder 100-2 compact, while ensuring areduction ratio required for a worm speed reduction mechanism. Also, forexample, a pitch circle of the worm gear 2 b is greater than a pitchcircle of the worm wheel 5 a.

In contrast, by setting a greater pitch circle of each of the worm gear1 d and the worm gear 2 b, a circumferential velocity of a tooth surfaceis increased, and thus frictional heat of the tooth surface might beincreased. Also, when the motor 200 operates at high speed, frictionalheat of the tooth surface might be also increased. The motor 200 andabsolute encoder 100-2 may be also used in a high-temperatureenvironment. In such a high-temperature environment, due to thermalexpansion of a given gear, backlash of the given gear is eliminated andthus tooth clogging might occur. In order to extend a life of theabsolute encoder 100-2, wear resistance of the tooth surface is requiredto be ensured. In view of the problem described above, the absoluteencoder 100-2 according to the second embodiment is desirably configuredas follows. In the following description, the configuration of theabsolute encoder 100-2 according to a modification of the firstembodiment will be described.

FIG. 34 is a plan view of the absolute encoder 100-2 according to themodification of the second embodiment. FIG. 35 is a cross-sectional viewof the absolute encoder taken along a plane that passes through thecentral axis of the intermediate gear 2. The absolute encoder 100-2according to the modification of the second embodiment differs from theabsolute encoder 100-2 according to the second embodiment, in the mainspindle gear 1 and the intermediate gear 2. Other configurations are thesame, and duplicate description is omitted.

As illustrated in FIG. 34, the intermediate gear 2 includes a firstintermediate gear part S8 including the worm wheel 2 a, and a secondintermediate gear part S9 including the worm gear 2 b.

As illustrated in FIG. 35, the first intermediate gear part S8 includesan insert portion S8 a. The insert portion S8 a is formed at a portionof the first intermediate gear part S8 toward one end thereof, and has acylindrical shape that is formed to extend in a direction of the centralaxis of the first intermediate gear part. The second intermediate gearpart S9 has an insert receiving portion S9 a into which the insertportion S8 a is inserted. The insert receiving portion S9 a is formed ata portion of the second intermediate gear part S9 toward one endthereof, and extends in a direction of the central axis of the secondintermediate gear part. The insert receiving portion S9 a has acylindrical shape that is formed so as to have a greater diameter thanthat of the insert portion S8 a. The insert receiving portion S9 a has abottom S9 b.

A bearing S10 is inserted into the insert receiving portion S9 a, andthe insert portion S8 a is further inserted into the insert receivingportion S9 a. The bearing S10 is disposed between the bottom S9 b and anend surface S8 b. Note that each of the end surface S8 b and the bottomS9 b contacts an outer ring of the bearing S10. The shaft 4 illustratedin FIG. 34 is inserted through an inner ring of the bearing S10. Bypress fit of the insert portion S8 a into the insert receiving portionS9 a, the first intermediate gear part S8 and the second intermediategear part S9 rotate in an integrated manner.

For example, the main spindle gear 1 including the worm gear 1 d, aswell as the second intermediate gear part S9 including the worm gear 2b, may be each formed using a first material. As the first material, forexample, an inorganic filler-containing PBT can be used.

Also, for example, the first intermediate gear part S8 including theworm wheel 2 a, as well as the layshaft gear 5 including the worm wheel5 a, may be each formed using a second material. As the second material,a POM natural without containing any filler or the like can be used.

A combination of members and materials is not limited to the combinationdescribed above. When the first intermediate gear part S8 and the mainspindle gear 1 are formed of different materials, it is particularlyeffective, because the first intermediate gear part and the main spindlegear may rotate at high speed.

Note that each of the first material and the second material is notlimited to a resinous material. As long as two types of materials havingdifferent characteristics, including a metallic material such as a brassmaterial, are used, the first material and the second material aresufficient.

Preferably, a coefficient of linear thermal expansion of material of oneamong the main spindle gear 1, including the worm gear 1 d, and thefirst intermediate gear part S8 including the worm wheel 2 a is lowerthan a coefficient of linear thermal expansion of a polyacetal resin.Thus, in comparison to a case where both the main spindle gear 1 and thefirst intermediate gear part S8 are each formed of a polyacetal resin,backlash between the worm gear 1 d and the worm wheel 2 a can beprevented from being eliminated even in a high-temperature environment,thereby preventing tooth clogging due to thermal expansion. Note thatwhen both the material of the main spindle gear 1 and the material ofthe first intermediate gear part S8 are each materials having a lowercoefficient of linear thermal expansion than that of a polyacetal resin,it is more preferable from the viewpoint of preventing the eliminationof backlash or tooth clogging due to thermal expansion.

More preferably, a coefficient of linear thermal expansion of thematerial of the main spindle gear 1 including the worm gear 1 d is lowerthan a coefficient of linear thermal expansion of a polyacetal resin.For example, in use in a high-temperature environment, because the wormgear 1 d having a great diameter is provided, a large absolute amount ofradial expansion is obtained in comparison to a case where a worm gearhaving a smaller diameter is provided. Thus, tooth clogging might occurdue to elimination of backlash. In view of the point described above,when as a material of the main spindle gear 1, a material having a lowcoefficient of linear thermal expansion is used, elimination of thetooth backlash is prevented more suitably. Accordingly, tooth cloggingcan be prevented.

Preferably, the material of at least one among the main spindle gear 1including the worm gear 1 d and the first intermediate gear part S8including the worm wheel 2 a is resin containing an inorganic filler. Byusing the resin containing an inorganic filler, a wear volume of theother material can be reduced. Thus, a life of the first wormspeed-changing mechanism can be extended.

Preferably, a melting point of the material of the main spindle gear 1including the worm gear 1 d is different from a melting point of thematerial of the first intermediate gear part S8 including the worm wheel2 a. For example, when the same material is used for two gears, in acase where a temperature of tooth surfaces thereof is greater than orequal to a given melting temperature, molten resins may mutually seize,thereby resulting in adhesion between the molten resins. In contrast,when materials having different melting points are respectively used fortwo gears, even if a melting point of one gear is reached, a meltingpoint of another gear is not reached, thereby allowing for reductions inpossibility of adhesion between the materials.

As described above, the relationship between the material of the mainspindle gear 1 including the worm gear 1 d and the material of the firstintermediate gear part S8 including the worm wheel 2 a has beendescribed. Likewise, the relationship described above can apply to therelationship between the material of the second intermediate gear partS9 including the worm gear 2 b and the material of the layshaft gear 5including the worm wheel 5 a.

Hereafter, the relationship between the material of the firstintermediate gear part S8 and the material of the second intermediategear part S9 will be described.

Preferably, a coefficient of linear thermal expansion of the material(first material, e.g., an inorganic filler-containing PBT) of the secondintermediate gear part S9 is lower than a coefficient of linear thermalexpansion of the material (second material, e.g., POM natural) of thefirst intermediate gear part S8. The insert portion S8 a of the firstintermediate gear part S8 is configured to be press-fitted into theinsert receiving portion S9 a of the second intermediate gear part S9.In such a manner, thermal expansion of the insert receiving portion S9 acan be lower than thermal expansion of the insert portion S1 a in thehigh-temperature environment. Thus, the effect of press fit can beprevented from being mitigated due to thermal expansion.

Preferably, tensile break strain of the material (first material, e.g.,inorganic filler-containing PBT) of the second intermediate gear partS9, which is to receive an insert, is smaller than tensile break strainof the material (second material, e.g., POM natural) of the firstintermediate gear part S8, which is to be inserted. Thus, when theintermediate gear 2 is assembled such that the insert receiving portionS9 a of the first intermediate gear part S8 is press-fitted into theinsert receiving portion S9 a of the second intermediate gear part S9,assembling of the first intermediate gear 2 is facilitated. Also, anegative change in inclination of the axial center of the intermediategear 2, relative to the shaft 4, due to decreases in stress, can bereduced.

Also, the bearing S10 is disposed at a connection portion at which theinsert portion S8 a is press-fitted into the insert receiving portion S9a. The second intermediate gear part S9 has a structure supported onboth sides of a given axial direction, by the bearings S3 and S10,thereby allowing for reductions in rattling in a radial direction of thesecond intermediate gear part. Also, for the first intermediate gearpart S8, the bearing S10 to be inserted into the insert receivingportion S9 a is press-fitted into the insert receiving portion S9 a, onthe insert portion S8 a-side, and thus rattling in the radial directioncan be reduced. Note that in the first intermediate gear part S8, theshaft receiving portion 2 c is formed on the side opposite the insertportion S8 a.

At a connection portion at which the insert portion S8 a is press-fittedinto the insert receiving portion S9 a, the bearing S10 having greaterstiffness than the first intermediate gear part S8 and the secondintermediate gear part S9 is disposed. In such a manner, the bearing S10serves as supports for supporting a structure of the intermediate gear2.

Moreover, in comparison to a case where the intermediate gear 2 thatincludes the worm wheel 2 a and the worm gear 2 b is molded integrally,for a case where the first intermediate gear part S8 including the wormwheel 2 a, as well as the second intermediate gear part S9 having theworm gear 2 b, are molded separately, for example, mold design forinjection molding is facilitated, thereby increasing productivity. Also,different materials can be respectively assigned to the worm wheel 2 aand the worm gear 2 b. FIG. 36 is a diagram illustrating a permanentmagnet 9A applicable to the absolute encoders 100-1 and 100-2 accordingto the first and second embodiments. FIG. 37 is a diagram illustrating apermanent magnet 9B applicable to the absolute encoders 100-1 and 100-2according to the first and second embodiments. In FIG. 36, the permanentmagnet 9A according to an example of a first configuration isillustrated. In the permanent magnet 9A, a first polar portion N havinga first polarity, as well as a second polar portion S having a secondpolarity different from the first polarity, are arranged in a radialdirection D1 of the permanent magnet 9A. In FIG. 37, the permanentmagnet 9B according to an example of a second configuration isillustrated. In the permanent magnet 9B, in an axial direction D2, asillustrated in the figure, of the permanent magnet 9B, a first polarportion N and a second polar portion S are arranged on the left side ofthe figure, relative to a middle portion of the permanent magnet 9B.Further, on the right side of the figure, a first polar portion N and asecond polar portion S are arranged in the axial direction D2, asillustrated in the figure, of the permanent magnet 9, in a manner suchthat the first polar portion N and the second polar portion S areinverted with respect to the case of the left side described above.Arrows “DM” illustrated in FIGS. 36 and 37 express magnetizationdirections.

Any one of the permanent magnet 9A and the permanent magnet 9B can beused as the permanent magnet 9 of each of the absolute encoders 100-1and 100-2 according to the first and second embodiments. However, in thepermanent magnet 9B, the magnetic field formed with a plurality ofmagnetic field lines is distributed so as to spread in the axialdirection D2, in comparison to the magnetic field generated through thepermanent magnet 9A. In contrast, in the permanent magnet 9A, themagnetic field formed with a plurality of magnetic field lines isdistributed so as to spread in the radial direction D1, in comparison tothe magnetic field generated through the permanent magnet 9B. In such acase, when the permanent magnet 9A is used in each of the absoluteencoders 100-1 and 100-2 according to the first and second embodiments,magnetic interference that influences the other magnetic sensor, asdescribed above, might be likely to occur due to the magnetic fieldgenerated so as to spread outward in the radial direction of thepermanent magnet 9A.

In the absolute encoders 100-1 and 100-2 according to the modificationsof the first and second embodiments, when the permanent magnet 9B isused as the permanent magnet 9, leakage magnetic flux generated from thepermanent magnet 9 does not appreciably influence the magnetic sensor50, in comparison to the case where the permanent magnet 9A is used.Also, when the permanent magnet 9B is used as the permanent magnet 8,leakage flux from the permanent magnet 8 does not appreciably influencethe magnetic sensor 40, in comparison to the case where the permanentmagnet 9A is used. As a result, reductions in accuracy in detecting arotation angle or a rotation amount of each of the layshaft gear 5 andthe main spindle gear 1 can be mitigated. Further, the absolute encoders100-1 and 100-2 can be made more compact, because reductions in accuracyin detecting the rotation angle or the rotation amount can be mitigated.

Note that the absolute encoder 100-1 according to the first embodimentis configured such that the central axes of the permanent magnets 8 andthe magnet holder 6 coincide with each other, as in the permanent magnet8 and the magnet holder 6 illustrated in FIG. 29. Also, the absoluteencoder 100-1 according to the first embodiment is configured such thatthe central axes of the permanent magnet 17 and the second layshaft gear138 coincide with each other, as in the permanent magnet 8 and themagnet holder 6 illustrated in FIG. 29. Further, the absolute encoder100-1 according to the first embodiment is configured such that thecentral axes of the permanent magnet 9 and the main spindle gear 1coincide with each other, as in the permanent magnet 9 and the mainspindle gear 1 illustrated in FIG. 30. With such a configuration, theabsolute encoder 100-1 according to the first embodiment can detect agiven rotation angle or a given rotation amount with higher accuracy.

Note that the configuration illustrated in one or more embodimentsdescribed above is an example of the present invention. Theconfiguration can be combined with another known technique.Alternatively, a portion of the configuration can be omitted or changedwithout departing from a spirit of the present invention.

Note that this International application claims priority under theJapanese Patent Application No. 2019-068909, filed Mar. 29, 2019, thecontents of which are incorporated herein by reference in theirentirety.

REFERENCE SIGNS LIST

-   1 main spindle gear, 1 a first cylindrical portion, 1 b second    cylindrical portion, 1 c communicating portion, 1 d worm gear, 1 e    bottom, 1 f press-fit portion, 1 g bottom, 1 h magnet holding    portion, 2 intermediate gear, 2 a worm wheel, 2 b worm gear, 2 c    shaft receiving portion, 2 d press-fit portion, 2 e sliding portion,    2 f bottom, 2 g through-hole, 3 bearing, 3 a outer ring, 3 b inner    ring, 3 c side surface, 3 d side surface, 4 shaft, 4 a one end, 4 b    the other end, 5 layshaft gear, 5-1 top, 5 a worm wheel, 5 b    through-hole, 6 magnet holder, 6 a magnet holding portion, 6 b    shaft, 6 c head, 7 bearing, 7 a outer ring, 7 b inner ring, 8    permanent magnet, 8 a surface, 9 permanent magnet, 9 a upper    surface, 9 b lower surface, 10 main base, 10-1 opening, 10-2 lower    surface, 10-3 wall surface, 10 a hole, 10 aa recessed portion, 10 ab    recessed portion, 10 ac recessed portion, 10 ad mounting surface, 10    ae screw hole, 10 b hole, 10 c contact surface, 10 d bearing holder,    10 da lower portion, 10 db upper portion, 10 dc inner peripheral    surface, 10 e leaf-spring mounting surface, 10 f screw hole, 10 g    substrate positioning pin, 10 gl base, 10 h distal end, 10 i stepped    portion, 10 j substrate positioning pin, 10 jl base, 10 k distal    end, 101 stepped portion, 10 m pillar, 10 p upper end surface, 10 q    pillar, 10 r upper end surface, 10 s pillar, 10 t upper end surface,    10 u screw hole, 10 v screw hole, 10 w screw hole, 11 leaf spring,    11 a sliding portion, lib mounting portion, 11 c hole, 11 d base, 12    screw, 13 substrate mounting screw, 14 screw, 15 case, 15-1 top    portion, 15A first side portion, 15B second side portion, 15C third    side portion, 15D fourth side portion, 15 a tab, 15 b tab, 15 c tab,    15 d hole, 15 e recessed portion, 15 f recessed portion, 15 g    recessed portion, 15 h connector case, 15 i opening, 16 mounted    screw, 17 permanent magnet, 20 substrate, 20-1 lower surface, 20-2    upper surface, 20 a positioning hole, 20 b positioning hole, 20 c    hole, 20 d hole, 20 e hole, 21 microcomputer, 21 b table processing    unit, 21 c rotation-amount determining unit, 21 e output unit, 21 p    rotation-angle acquiring unit, 21 q rotation-angle acquiring unit,    22 bidirectional driver, 23 line driver, 24 connector, 40 magnetic    sensor, 40 a surface, 50 magnetic sensor, 50 a surface, 60 base, 61    magnetic flux shielding portion, 61 first plate surface, 61 a second    plate surface, 61 c first end surface, 61 d second end surface, 61 e    third end surface, 62 magnetic flux shielding portion, 62 a first    plate surface, 62 b second end surface, 62 c first end surface, 62 d    second end surface, 62 e third end surface, 164 screw, 70 wall, 71    wall, 72 wall, 73 side surface, 80 wall, 90 magnetic sensor, 100-1    absolute encoder, 100-2 absolute encoder, 101 main spindle gear, 101    a first cylindrical portion, 101 b disk portion, 101 c worm gear,    101 d magnet holding portion, 102 first intermediate gear, 102 a    worm wheel, 102 b first worm gear, 102 c base, 102 d first    cylindrical portion, 102 e second cylindrical portion, 102 f third    cylindrical portion, 102 g hemispherical protrusion, 102 h second    worm gear, 102 i sliding portion, 105 first layshaft gear, 105 a    worm wheel, 105 b shaft receiving portion, 105 c disk portion, 105 d    holding portion, 106 shaft, 110 main base, 110 a base, 110 b    supporting portion, 110 c supporting portion, 107 stopper ring, 108    stopper ring, 110-1 opening, 110-1 a wall surface, 111 leaf spring,    111 a sliding portion, 1 l 1 b mounting portion, 115 case, 115 a    outer wall, 115 c outer wall, 115 d outer wall, 116 cover, 120    substrate, 121 microcomputer, 121 b table processing unit, 121 c    rotation-amount determining unit, 121 e output unit, 121 p    rotation-angle acquiring unit, 121 q rotation-angle acquiring unit,    121 r rotation-angle acquiring unit, 133 second intermediate gear,    133 a worm wheel, 133 b shaft receiving portion, 133 c extended    portion, 133 d fourth drive gear, 138 second layshaft gear, 138 a    fourth driven gear, 138 b shaft receiving portion, 138 c extended    portion, 138 d magnet holding portion, 139 shaft, 141 pillar, 200    motor, 201 motor shaft, 202 housing, 202 a cut-out portion, 301    first side, 302 second side, 303 third side, 304 fourth side, 400    connector, 500 magnetic flux shielding portion, 500 a first plate    surface, 500 b second plate surface, 500 c first end surface, 500 d    second end surface, 500 e third end surface, 501 magnetic flux    shielding portion, 501 a distal end surface, 502 magnetic flux    shielding portion, 502 a distal end surface, Td axial direction of    each of intermediate gear 2 and shaft 4, S1, S2, S3, S6, S7, S8, S9,    intermediate gear part, S4, S5, S10 bearing, S1 a, S1 b, S8 a insert    portion, S2 a, S3 a, S9 a insert receiving portion

1. An absolute encoder comprising: a first drive gear configured torotate in accordance with rotation of a main spindle; and a first drivengear of which a central axis is perpendicular to a central axis of thefirst drive gear, the first driven gear engaging with the first drivegear, wherein the first drive gear is formed using a first material, andwherein the first driven gear is formed using a second materialdifferent from the first material.
 2. The absolute encoder according toclaim 1, wherein the first drive gear is a worm gear, and wherein thefirst driven gear is a worm wheel.
 3. The absolute encoder according toclaim 1, wherein a coefficient of linear thermal expansion of one amongthe first material and the second material is lower than a coefficientof linear thermal expansion of a polyacetal resin.
 4. The absoluteencoder according to claim 1, wherein the first material is a resincontaining a filler.
 5. The absolute encoder according to claim 1,wherein a melting point of the first material is different from amelting point of the second material.
 6. The absolute encoder accordingto claim 1, wherein the first material is a polyacetal resin containingan inorganic filler, and wherein the second material is a polyacetalresin.
 7. The absolute encoder according to claim 1, further comprising:a second drive gear coaxially provided with the first driven gear, thesecond drive gear being configured to rotate in accordance with rotationof the first driven gear; and a second driven gear of which a centralaxis is perpendicular to a central axis of the first driven gear, thesecond driven gear engaging with the second drive gear, wherein thesecond drive gear is formed using the first material, and wherein thesecond driven gear is formed using the second material.
 8. The absoluteencoder according to claim 7, wherein the second drive gear is a wormgear, and wherein the second driven gear is a worm wheel.
 9. Theabsolute encoder according to claim 7, wherein the first driven gearincludes an insert portion, and wherein the second drive gear includesan insert receiving portion into which the insert portion is inserted.10. The absolute encoder according to claim 9, further comprising abearing inserted into the insert receiving portion and disposed betweena bottom of the insert receiving portion and an end surface of theinsert portion.
 11. The absolute encoder according to claim 9, whereinthe insert portion is press-fitted into the insert receiving portion,and wherein tensile break stress of the first material is less thantensile break stress of the second material.